Atoms and Molecules MCQ Class 9

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Atoms and Molecules MCQ Class 9. These 100 Multiple Choice Questions with Answer and Explanation will help you score full marks in your class 9 Science exam.

Atoms and Molecules MCQ Class 9

Historical Background and Philosophical Theories (MCQ 1 to 10)

Ancient Indian Philosophy

Question 1: Who proposed the concept of Parmanu in ancient Indian philosophy?
A. Democritus
B. Leucippus
C. Maharishi Kanad
D. Pakudha Katyayama

Answer
Answer: Maharishi Kanad proposed the concept of Parmanu, which refers to the smallest, indivisible particle of matter.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 2: What idea did Pakudha Katyayama contribute to Indian philosophy?
A. The indivisibility of atoms
B. That particles exist in a combined form
C. The laws of chemical combination
D. The theory of mass conservation

Answer
Answer: Pakudha Katyayama contributed the idea that particles exist in a combined form to create various forms of matter.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Ancient Greek Philosophers

Question 3: Which Greek philosopher is known for suggesting the indivisibility of matter into atoms?
A. Leucippus
B. Democritus
C. Aristotle
D. Plato

Answer
Answer: Democritus, along with Leucippus, suggested that matter could be divided until the smallest indivisible particles, atoms, remain.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 4: What did Democritus call the smallest indivisible particles?
A. Atoms
B. Parmanu
C. Electrons
D. Molecules

Answer
Answer: Democritus called the smallest indivisible particles atoms, meaning indivisible.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 5: How was the idea of atoms viewed in ancient times?
A. Based on experiments
B. Philosophical and unverified
C. Proven by scientific research
D. Rejected by all philosophers

Answer
Answer: The idea of atoms was based on philosophical considerations and lacked experimental verification until the 18th century.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 6: What philosophical question was central to both Indian and Greek ancient philosophers?
A. The creation of the universe
B. The divisibility of matter
C. The structure of the atom
D. The concept of energy

Answer
Answer: The divisibility of matter was a central question explored by both Indian and Greek ancient philosophers.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 7: What era did Maharishi Kanad propose the idea of Parmanu?
A. 400 BC
B. 300 BC
C. 500 BC
D. 600 BC

Answer
Answer: Maharishi Kanad proposed the idea of Parmanu around 500 BC.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 8: Which Indian philosopher emphasized the combination of particles in matter?
A. Maharishi Kanad
B. Pakudha Katyayama
C. Aristotle
D. Democritus

Answer
Answer: Pakudha Katyayama emphasized the idea that particles exist in a combined form to create matter.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 9: In ancient times, what was the main challenge in proving the existence of atoms?
A. Lack of tools
B. Philosophical disagreements
C. Absence of experimental validation
D. Limited resources

Answer
Answer: The main challenge in proving the existence of atoms was the absence of experimental validation.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 10: Which ancient civilization believed that matter could eventually be broken down into indivisible particles?
A. Chinese
B. Egyptian
C. Indian and Greek
D. Roman

Answer
Answer: Both Indian and Greek civilizations believed that matter could be broken down into indivisible particles.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Laws of Chemical Combination (MCQ 11 to 20) -Atoms and Molecules MCQ Class 9

Law of Conservation of Mass

Question 11: Who is credited with establishing the Law of Conservation of Mass?
A. Democritus
B. John Dalton
C. Antoine Lavoisier
D. Joseph Proust

Answer
Answer: Antoine Lavoisier is credited with establishing the Law of Conservation of Mass.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 12: What does the Law of Conservation of Mass state?
A. Mass can be created in a chemical reaction
B. Mass remains unchanged during a chemical reaction
C. Mass can only be destroyed in a chemical reaction
D. Mass is irrelevant to chemical reactions

Answer
Answer: The Law of Conservation of Mass states that mass remains unchanged during a chemical reaction.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 13: In a closed system, what happens to the mass before and after a chemical reaction?
A. It decreases
B. It increases
C. It remains constant
D. It fluctuates

Answer
Answer: In a closed system, the mass remains constant before and after a chemical reaction.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 14: How was the Law of Conservation of Mass experimentally demonstrated?
A. By using light
B. By using chemical reactions
C. By using magnets
D. By measuring volume

Answer
Answer: The Law of Conservation of Mass was experimentally demonstrated by using chemical reactions.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 15: What is essential for verifying the Law of Conservation of Mass during an experiment?
A. Keeping the system open
B. Using different chemicals
C. Ensuring a closed system
D. Using an electronic balance

Answer
Answer: Ensuring a closed system is essential for verifying the Law of Conservation of Mass during an experiment.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Law of Constant Proportions

Question 16: What does the Law of Constant Proportions state?
A. Compounds have the same elements in the same proportions by mass
B. Compounds can have varying elements
C. The mass of elements can change depending on the source
D. Compounds form randomly

Answer
Answer: The Law of Constant Proportions states that compounds have the same elements in the same proportions by mass.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 17: Who is credited with formulating the Law of Constant Proportions?
A. Antoine Lavoisier
B. Joseph Proust
C. John Dalton
D. Isaac Newton

Answer
Answer: Joseph Proust is credited with formulating the Law of Constant Proportions.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 18: Which compound exemplifies the Law of Constant Proportions?
A. Sodium chloride
B. Water
C. Hydrogen gas
D. Sodium carbonate

Answer
Answer: Water exemplifies the Law of Constant Proportions as it always contains hydrogen and oxygen in a 1:8 mass ratio.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 19: What happens when 9 g of water is decomposed?
A. 8 g of hydrogen and 1 g of oxygen are formed
B. 1 g of hydrogen and 8 g of oxygen are formed
C. 5 g of hydrogen and 4 g of oxygen are formed
D. No change in mass

Answer
Answer: When 9 g of water is decomposed, 1 g of hydrogen and 8 g of oxygen are formed.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 20: Which gas is always present in ammonia in the ratio 14:3 by mass with hydrogen?
A. Oxygen
B. Nitrogen
C. Carbon
D. Sulphur

Answer
Answer: Nitrogen is always present in ammonia in the ratio 14:3 by mass with hydrogen.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Dalton’s Atomic Theory (MCQ 21 to 30) – Atoms and Molecules MCQ Class 9

Postulates of Dalton’s Atomic Theory

Question 21: What is the basic concept of Dalton’s atomic theory?
A. All matter is composed of molecules
B. All matter is composed of indivisible particles called atoms
C. All matter is composed of electrons
D. All matter is composed of energy

Answer
Answer: All matter is composed of indivisible particles called atoms, as per Dalton’s atomic theory.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 22: According to Dalton’s atomic theory, atoms of the same element are:
A. Different in mass and properties
B. Identical in mass and chemical properties
C. Larger than molecules
D. Smaller than protons

Answer
Answer: Atoms of the same element are identical in mass and chemical properties according to Dalton’s atomic theory.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 23: Dalton’s atomic theory states that atoms of different elements have:
A. Different masses and chemical properties
B. The same masses but different properties
C. The same properties but different charges
D. Identical masses and properties

Answer
Answer: Atoms of different elements have different masses and chemical properties.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 24: According to Dalton’s atomic theory, atoms combine in:
A. Large ratios
B. Random ratios
C. Fixed, small whole number ratios
D. Changing ratios

Answer
Answer: Atoms combine in fixed, small whole number ratios to form compounds.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 25: Which of the following is NOT a postulate of Dalton’s atomic theory?
A. Atoms are indivisible
B. Atoms can be destroyed in chemical reactions
C. Atoms of a given element are identical
D. Atoms participate in chemical reactions

Answer
Answer: Dalton’s theory postulates that atoms cannot be destroyed in chemical reactions.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Applications of Dalton’s Theory

Question 26: Which law does Dalton’s atomic theory explain regarding the conservation of matter?
A. Law of Constant Proportions
B. Law of Multiple Proportions
C. Law of Conservation of Mass
D. Law of Electrostatics

Answer
Answer: Dalton’s atomic theory explains the Law of Conservation of Mass.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 27: How does Dalton’s atomic theory explain the Law of Constant Proportions?
A. Atoms of different elements combine in fixed ratios
B. Atoms combine randomly
C. Atoms do not interact chemically
D. Atoms can combine in any ratio

Answer
Answer: Dalton’s atomic theory explains the Law of Constant Proportions by stating that atoms of different elements combine in fixed ratios.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 28: Dalton’s atomic theory helped in understanding which fundamental principle of chemistry?
A. Law of Indestructibility
B. Law of Gravity
C. Laws of Chemical Combination
D. Laws of Magnetism

Answer
Answer: Dalton’s atomic theory helped in understanding the Laws of Chemical Combination.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 29: What is a key limitation of Dalton’s atomic theory?
A. Atoms are actually divisible into smaller particles
B. Atoms cannot participate in chemical reactions
C. Atoms do not combine in small whole number ratios
D. Atoms of the same element are always different

Answer
Answer: A key limitation of Dalton’s atomic theory is that atoms are actually divisible into smaller particles.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 30: According to Dalton’s theory, what remains constant in a given compound?
A. The shape of atoms
B. The type of chemical reactions
C. The relative number and kinds of atoms
D. The energy level of atoms

Answer
Answer: The relative number and kinds of atoms remain constant in a given compound.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Structure of Atoms (MCQ 31 to 40) – Atoms and Molecules MCQ Class 9

Size and Scale of Atoms

Question 31: How is atomic size typically measured?
A. In kilograms
B. In centimeters
C. In nanometers
D. In millimeters

Answer
Answer: Atomic size is typically measured in nanometers.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 32: What is the approximate size of a hydrogen atom?
A. 10⁻¹⁰ meters
B. 10⁻⁵ meters
C. 1 meter
D. 10 meters

Answer
Answer: The approximate size of a hydrogen atom is 10⁻¹⁰ meters.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 33: How does the size of an atom compare to common objects?
A. Atoms are larger than grains of sand
B. Atoms are about the same size as an apple
C. Atoms are much smaller than common objects
D. Atoms are as large as a molecule of water

Answer
Answer: Atoms are much smaller than common objects, such as grains of sand or apples.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 34: How many hydrogen atoms would approximately fit across the thickness of a sheet of paper?
A. 100
B. 10
C. 1 million
D. 1 billion

Answer
Answer: Approximately 1 million hydrogen atoms would fit across the thickness of a sheet of paper.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Atomic Symbols

Question 35: Who introduced the first symbols for chemical elements?
A. Antoine Lavoisier
B. John Dalton
C. Democritus
D. Joseph Proust

Answer
Answer: John Dalton introduced the first symbols for chemical elements.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 36: How are modern symbols for elements represented?
A. Using numbers only
B. Using one or two letters
C. Using shapes
D. Using full names of elements

Answer
Answer: Modern symbols for elements are represented using one or two letters.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 37: According to IUPAC guidelines, what is the first letter of an element’s symbol?
A. Always a lowercase letter
B. Always an uppercase letter
C. It can be either uppercase or lowercase
D. Always a number

Answer
Answer: According to IUPAC guidelines, the first letter of an element’s symbol is always an uppercase letter.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 38: Which element’s symbol is derived from its Latin name ferrum?
A. Sodium
B. Potassium
C. Iron
D. Copper

Answer
Answer: The symbol for iron (Fe) is derived from its Latin name ferrum.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 39: What is the correct symbol for sodium?
A. Sa
B. Na
C. So
D. N

Answer
Answer: The correct symbol for sodium is Na.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 40: What does the modern system for naming elements follow?
A. Dalton’s recommendations
B. A traditional naming system
C. IUPAC guidelines
D. Greek philosopher guidelines

Answer
Answer: The modern system for naming elements follows IUPAC guidelines.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Atomic Mass (MCQ 41 to 50) – Atoms and Molecules MCQ Class 9

Concept of Atomic Mass

Question 41: What is the definition of atomic mass?
A. The number of electrons in an atom
B. The average mass of an atom compared to 1/12th the mass of one carbon-12 atom
C. The volume of an atom
D. The size of an atom

Answer
Answer: The atomic mass is the average mass of an atom compared to 1/12th the mass of one carbon-12 atom.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 42: What is the unit used to express atomic mass?
A. Grams
B. Kilograms
C. Atomic mass unit (amu)
D. Joules

Answer
Answer: The atomic mass is expressed in atomic mass units (amu).(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 43: Which isotope is used as the standard reference for atomic mass?
A. Oxygen-16
B. Carbon-12
C. Hydrogen-1
D. Nitrogen-14

Answer
Answer: Carbon-12 is used as the standard reference for atomic mass.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 44: Why was carbon-12 chosen as the reference for atomic mass?
A. It forms compounds with many elements
B. It was easier to measure
C. It reacts with oxygen
D. It is abundant in nature

Answer
Answer: Carbon-12 was chosen as the reference for atomic mass because it forms compounds with many elements and its mass is convenient for calculations.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 45: How is atomic mass measured in terms of carbon-12?
A. As one-tenth the mass of a carbon-12 atom
B. As half the mass of a carbon-12 atom
C. As one-twelfth the mass of a carbon-12 atom
D. As the full mass of a carbon-12 atom

Answer
Answer: Atomic mass is measured as one-twelfth the mass of a carbon-12 atom.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Atomic Masses of Common Elements

Question 46: What is the atomic mass of hydrogen?
A. 2 u
B. 16 u
C. 12 u
D. 1 u

Answer
Answer: The atomic mass of hydrogen is 1 u.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 47: What is the atomic mass of oxygen?
A. 1 u
B. 16 u
C. 12 u
D. 24 u

Answer
Answer: The atomic mass of oxygen is 16 u.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 48: Which element has an atomic mass of 23 u?
A. Sodium
B. Magnesium
C. Nitrogen
D. Calcium

Answer
Answer: Sodium has an atomic mass of 23 u.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 49: What is the atomic mass of chlorine?
A. 12 u
B. 40 u
C. 35.5 u
D. 1 u

Answer
Answer: The atomic mass of chlorine is 35.5 u.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 50: How can the atomic mass of an element be calculated?
A. By measuring its volume
B. By counting the number of protons
C. By using chemical reactions and comparing it to carbon-12
D. By observing its color

Answer
Answer: The atomic mass of an element can be calculated by using chemical reactions and comparing it to carbon-12.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Molecules and Atomicity (MCQ 51 to 60) – Atoms and Molecules MCQ Class 9

Molecules of Elements

Question 51: What is a diatomic molecule?
A. A molecule made of two different elements
B. A molecule with two atoms of the same element
C. A molecule with three atoms of the same element
D. A molecule with one atom

Answer
Answer: A diatomic molecule is a molecule with two atoms of the same element.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 52: Which of the following is a diatomic molecule?
A. Oxygen (O₂)
B. Phosphorus (P₄)
C. Sulphur (S₈)
D. Carbon dioxide (CO₂)

Answer
Answer: Oxygen (O₂) is a diatomic molecule.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 53: What is a polyatomic molecule?
A. A molecule with more than two atoms
B. A molecule with only one atom
C. A molecule with only two atoms
D. A molecule with one proton

Answer
Answer: A polyatomic molecule is a molecule with more than two atoms.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 54: Which of the following is an example of a polyatomic molecule?
A. Oxygen (O₂)
B. Phosphorus (P₄)
C. Hydrogen (H₂)
D. Helium (He)

Answer
Answer: Phosphorus (P₄) is an example of a polyatomic molecule.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Molecules of Compounds

Question 55: What defines a molecule of a compound?
A. Combination of two or more atoms of the same element
B. Combination of atoms of different elements in fixed proportions
C. A group of electrons held together
D. A single atom of an element

Answer
Answer: A molecule of a compound is defined by the combination of atoms of different elements in fixed proportions.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 56: Which of the following is an example of a compound?
A. Oxygen (O₂)
B. Water (H₂O)
C. Phosphorus (P₄)
D. Nitrogen (N₂)

Answer
Answer: Water (H₂O) is an example of a compound.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 57: In water (H₂O), what is the proportion of hydrogen to oxygen by mass?
A. 1:1
B. 2:1
C. 1:8
D. 1:3

Answer
Answer: In water, the proportion of hydrogen to oxygen by mass is 1:8.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Ions and Polyatomic Ions

Question 58: What is an ion?
A. A molecule
B. A charged particle
C. A neutral atom
D. A mixture of elements

Answer
Answer: An ion is a charged particle.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 59: Which of the following is a positively charged ion (cation)?
A. Cl⁻
B. SO₄²⁻
C. Na⁺
D. O²⁻

Answer
Answer: Na⁺ is a positively charged ion (cation).(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 60: What is a polyatomic ion?
A. An ion formed by a single atom
B. A group of atoms carrying a charge
C. A neutral molecule
D. An atom with a high mass

Answer
Answer: A polyatomic ion is a group of atoms carrying a charge.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Writing Chemical Formulae (MCQ 61 to 70) – Atoms and Molecules MCQ Class 9

Valency

Question 61: What is valency?
A. The atomic mass of an element
B. The ability of an atom to form bonds with other atoms
C. The number of electrons in an atom
D. The speed at which a reaction occurs

Answer
Answer: Valency is the ability of an atom to form bonds with other atoms.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 62: How is the chemical formula of a compound determined?
A. By using the atomic number of the elements
B. By using valency to balance the charges of atoms
C. By using the volume of the atoms
D. By using the color of the elements

Answer
Answer: The chemical formula of a compound is determined by using valency to balance the charges of atoms.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 63: What is the valency of sodium (Na) in NaCl?
A. 2
B. 3
C. 1
D. 4

Answer
Answer: The valency of sodium (Na) in NaCl is 1.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Formula of Simple Compounds

Question 64: How is the formula for sodium chloride written?
A. Na₂Cl
B. NaCl₂
C. NaCl
D. Cl₂Na

Answer
Answer: The formula for sodium chloride is written as NaCl.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 65: What is the formula for magnesium chloride?
A. MgCl
B. MgCl₂
C. Mg₂Cl
D. ClMg

Answer
Answer: The formula for magnesium chloride is MgCl₂.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Formula of Polyatomic Compounds

Question 66: How is the formula for calcium hydroxide written?
A. CaOH
B. CaOH₂
C. Ca(OH)₂
D. Ca₂OH

Answer
Answer: The correct formula for calcium hydroxide is Ca(OH)₂.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 67: How is the formula for aluminium sulphate written?
A. Al(SO₄)₃
B. Al₂(SO₄)₃
C. AlSO₄
D. Al₂SO₄

Answer
Answer: The correct formula for aluminium sulphate is Al₂(SO₄)₃.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 68: Why are brackets used in the formula of calcium hydroxide, Ca(OH)₂?
A. To show that the compound contains polyatomic ions
B. To indicate the presence of two oxygen atoms
C. To distinguish between calcium and oxygen
D. To simplify the chemical formula

Answer
Answer: Brackets are used in the formula of calcium hydroxide to show that the compound contains polyatomic ions.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 69: What is the chemical formula for ammonium carbonate?
A. (NH₄)CO₃
B. (NH₄)₂CO₃
C. NH₄CO₃
D. NH₄₂CO₃

Answer
Answer: The correct chemical formula for ammonium carbonate is (NH₄)₂CO₃.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 70: What is the correct formula for potassium nitrate?
A. KNO₃
B. K₂NO₃
C. K(NO₃)₂
D. K₂N

Answer
Answer: The correct formula for potassium nitrate is KNO₃.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Molecular Mass and Formula Unit Mass (MCQ 71 to 80)

Molecular Mass

Question 71: What is molecular mass?
A. The mass of a single atom
B. The sum of the atomic masses of all atoms in a molecule
C. The total volume of a molecule
D. The number of atoms in a molecule

Answer
Answer: The molecular mass is the sum of the atomic masses of all atoms in a molecule.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 72: How is molecular mass measured?
A. In grams
B. In kilograms
C. In atomic mass units (u)
D. In milliliters

Answer
Answer: Molecular mass is measured in atomic mass units (u).(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 73: What is the molecular mass of water (H₂O)?
A. 18 u
B. 16 u
C. 20 u
D. 10 u

Answer
Answer: The molecular mass of water (H₂O) is 18 u.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 74: How do you calculate the molecular mass of carbon dioxide (CO₂)?
A. Add the masses of one carbon atom and two oxygen atoms
B. Add the masses of two carbon atoms and one oxygen atom
C. Add the masses of one carbon atom and one oxygen atom
D. Add the mass of one carbon atom only

Answer
Answer: To calculate the molecular mass of carbon dioxide, add the masses of one carbon atom and two oxygen atoms.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 75: Which of the following has a molecular mass of 17 u?
A. Ammonia (NH₃)
B. Water (H₂O)
C. Oxygen (O₂)
D. Carbon dioxide (CO₂)

Answer
Answer: Ammonia (NH₃) has a molecular mass of 17 u.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 76: What is the molecular mass of nitrogen gas (N₂)?
A. 14 u
B. 28 u
C. 44 u
D. 18 u

Answer
Answer: The molecular mass of nitrogen gas (N₂) is 28 u.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Formula Unit Mass

Question 77: What is formula unit mass?
A. The mass of one molecule
B. The mass of a single atom
C. The sum of the atomic masses in a formula unit of an ionic compound
D. The total number of ions in a compound

Answer
Answer: Formula unit mass is the sum of the atomic masses in a formula unit of an ionic compound.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 78: What is the formula unit mass of sodium chloride (NaCl)?
A. 45.5 u
B. 58.5 u
C. 23 u
D. 35.5 u

Answer
Answer: The formula unit mass of sodium chloride (NaCl) is 58.5 u.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 79: How do you calculate the formula unit mass of calcium chloride (CaCl₂)?
A. Add the atomic mass of calcium to the atomic masses of two chlorine atoms
B. Add the atomic mass of one calcium and one chlorine atom
C. Multiply the atomic mass of calcium by two
D. Add the atomic masses of two calcium and one chlorine atom

Answer
Answer: To calculate the formula unit mass of calcium chloride (CaCl₂), add the atomic mass of calcium to the atomic masses of two chlorine atoms.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 80: Which of the following is an example of a substance with a formula unit mass?
A. H₂O
B. NaCl
C. NH₃
D. O₂

Answer
Answer: NaCl is an example of a substance with a formula unit mass.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Questions on the Laws of Chemical Combination (MCQ 81 to 85)

Question 81: Which law explains that mass is conserved during a chemical reaction?
A. Law of Constant Proportions
B. Law of Multiple Proportions
C. Law of Conservation of Mass
D. Law of Electromagnetism

Answer
Answer: The Law of Conservation of Mass explains that mass is conserved during a chemical reaction.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 82: How does the Law of Constant Proportions apply to water (H₂O)?
A. Water contains hydrogen and oxygen in different ratios
B. Water always contains hydrogen and oxygen in a 1:8 ratio by mass
C. Water has no fixed proportion of elements
D. Water contains hydrogen and nitrogen

Answer
Answer: The Law of Constant Proportions applies to water as it always contains hydrogen and oxygen in a 1:8 ratio by mass.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 83: In which chemical reaction does the Law of Conservation of Mass hold true?
A. Burning of wood
B. Dissolving sugar in water
C. Formation of carbon dioxide from carbon and oxygen
D. Melting of ice

Answer
Answer: The Law of Conservation of Mass holds true in the formation of carbon dioxide from carbon and oxygen.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 84: Which scientist is associated with the Law of Conservation of Mass?
A. John Dalton
B. Joseph Proust
C. Antoine Lavoisier
D. Isaac Newton

Answer
Answer: Antoine Lavoisier is associated with the Law of Conservation of Mass.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 85: What does the Law of Constant Proportions state about compounds?
A. Compounds have varying compositions depending on conditions
B. Compounds always have the same elements in the same proportions by mass
C. Compounds change their proportions when heated
D. Compounds are made up of the same element

Answer
Answer: The Law of Constant Proportions states that compounds always have the same elements in the same proportions by mass.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Questions on Writing Chemical Formulae (MCQ 86 to 90)

Question 86: How is the formula for calcium oxide written?
A. CaO₂
B. CaO
C. CO
D. Ca₂O

Answer
Answer: The formula for calcium oxide is written as CaO.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 87: What is the correct formula for sodium carbonate?
A. Na₂CO₃
B. NaCO₂
C. Na₃CO₂
D. NaC₂O₄

Answer
Answer: The correct formula for sodium carbonate is Na₂CO₃.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 88: Which of the following is the formula for ammonium sulphate?
A. (NH₄)SO₄
B. NH₄SO₄
C. (NH₄)₂SO₄
D. NH₄₂SO₄

Answer
Answer: The formula for ammonium sulphate is (NH₄)₂SO₄.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 89: How is the formula for magnesium chloride written?
A. MgCl
B. MgCl₂
C. Mg₂Cl
D. MgCl₃

Answer
Answer: The formula for magnesium chloride is written as MgCl₂.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 90: What is the chemical formula for aluminium oxide?
A. Al₂O₃
B. AlO
C. AlO₂
D. Al₃O₂

Answer
Answer: The chemical formula for aluminium oxide is Al₂O₃.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Calculation of Molecular and Formula Unit Masses (MCQ 91 to 100)

Question 91: How do you calculate the molecular mass of methane (CH₄)?
A. Add the atomic mass of one carbon and four hydrogen atoms
B. Multiply the mass of carbon by four
C. Multiply the mass of hydrogen by four
D. Add the atomic masses of two hydrogen and two carbon atoms

Answer
Answer: To calculate the molecular mass of methane (CH₄), add the atomic mass of one carbon and four hydrogen atoms.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 92: What is the molecular mass of oxygen (O₂)?
A. 32 u
B. 16 u
C. 28 u
D. 44 u

Answer
Answer: The molecular mass of oxygen (O₂) is 32 u.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 93: What is the formula unit mass of calcium chloride (CaCl₂)?
A. 40 u
B. 58.5 u
C. 111 u
D. 22.4 u

Answer
Answer: The formula unit mass of calcium chloride (CaCl₂) is 111 u.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 94: What is the molecular mass of carbon dioxide (CO₂)?
A. 12 u
B. 28 u
C. 44 u
D. 56 u

Answer
Answer: The molecular mass of carbon dioxide (CO₂) is 44 u.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 95: Which substance has a molecular mass of 18 u?
A. Carbon dioxide (CO₂)
B. Oxygen (O₂)
C. Water (H₂O)
D. Methane (CH₄)

Answer
Answer: Water (H₂O) has a molecular mass of 18 u.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 96: What is the formula unit mass of sodium chloride (NaCl)?
A. 45.5 u
B. 58.5 u
C. 23 u
D. 40 u

Answer
Answer: The formula unit mass of sodium chloride (NaCl) is 58.5 u.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 97: How do you calculate the molecular mass of hydrogen (H₂)?
A. Add the mass of one hydrogen atom
B. Multiply the mass of hydrogen by two
C. Add the mass of two oxygen atoms
D. Subtract the mass of one hydrogen atom

Answer
Answer: To calculate the molecular mass of hydrogen (H₂), multiply the mass of hydrogen by two.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 98: What is the molecular mass of ammonia (NH₃)?
A. 17 u
B. 18 u
C. 44 u
D. 32 u

Answer
Answer: The molecular mass of ammonia (NH₃) is 17 u.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 99: What is the formula unit mass of magnesium chloride (MgCl₂)?
A. 40 u
B. 58.5 u
C. 95.5 u
D. 111 u

Answer
Answer: The formula unit mass of magnesium chloride (MgCl₂) is 95.5 u.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Question 100: What is the molecular mass of ethanol (C₂H₅OH)?
A. 34 u
B. 44 u
C. 46 u
D. 56 u

Answer
Answer: The molecular mass of ethanol (C₂H₅OH) is 46 u.(Atoms and Molecules MCQ Class 9 by Top100MCQ.com)
   

Read Also: India – Size and Location – Class 9 MCQs – Best 100

Most Asked Questions: Atoms and Molecules Class 9

What is the Law of Conservation of Mass?

The Law of Conservation of Mass states that mass can neither be created nor destroyed during a chemical reaction.

What is the Law of Constant Proportions?

The Law of Constant Proportions states that in a chemical compound, the elements are always present in definite proportions by mass.

What are the main postulates of Dalton’s Atomic Theory?

All matter is made of atoms, which are indivisible.
Atoms of the same element are identical.
Atoms of different elements have different masses and properties.
Atoms combine in fixed whole-number ratios to form compounds.
Atoms cannot be created or destroyed in chemical reactions.

How is atomic mass defined?

Atomic mass is the average mass of an atom compared to 1/12th the mass of a carbon-12 atom, measured in atomic mass units (u).

What is the difference between a molecule and an ion?

A molecule is a group of atoms chemically bonded together, while an ion is a charged particle formed when an atom or a group of atoms gains or loses electrons.

Quick Revision: Atoms and Molecules MCQ Class 9

Key LearningSummary
Philosophical TheoriesIndian philosophers like Maharishi Kanad and Greek philosophers such as Democritus suggested the indivisibility of matter into particles like Parmanu or atoms.
Law of Conservation of MassThis law states that mass can neither be created nor destroyed in a chemical reaction.
Law of Constant ProportionsElements combine in fixed proportions by mass to form compounds, as demonstrated by water and ammonia.
Dalton’s Atomic TheoryMatter is composed of indivisible atoms that combine in fixed whole-number ratios to form compounds.
Atomic SizeAtoms are extremely small and measured in nanometers, making them far smaller than any object we can compare.
Atomic SymbolsModern element symbols follow IUPAC guidelines, using one or two letters, such as H for hydrogen or Na for sodium.
Atomic MassAtomic mass is defined relative to 1/12th the mass of a carbon-12 atom and expressed in atomic mass units (u).
Molecules and AtomicityMolecules are groups of atoms bonded together. They can be diatomic (O₂) or polyatomic (P₄).
IonsIons are charged particles formed when atoms lose or gain electrons, resulting in cations (positive) or anions (negative).
Valency and Chemical FormulaeValency determines how atoms combine. Chemical formulas are derived based on the valency and charge balancing, e.g., NaCl, Ca(OH)₂.
Molecular Mass and Formula Unit MassMolecular mass is calculated by summing the atomic masses of all atoms in a molecule, while formula unit mass applies to ionic compounds like NaCl.
Polyatomic IonsIons formed by groups of atoms, like SO₄²⁻, play a key role in forming complex compounds.

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