Class 9 Science: Atoms and Molecules Quiz

Which of the following laws states that a chemical compound always contains the same elements in definite proportions by mass?

• Law of Conservation of Mass

• Law of Definite Proportions

• Dalton's Atomic Theory

• Law of Multiple Proportions

The molecular formula of water is H₂O. What is the ratio of hydrogen and oxygen by mass in water?

• 1:2

• 2:1

• 8:1

• 1:8

Which of these statements is NOT a postulate of Dalton's Atomic Theory?

• Atoms can be created and destroyed in a chemical reaction.

• Atoms of different elements combine in fixed whole-number ratios.

• Atoms are indivisible particles.

• The mass of an atom can vary within the same element.

Which of the following is a triatomic molecule?

• O₂

• CO₂

• H₂

• NaCl

What is the formula of a compound formed when calcium and oxygen combine?

• CaO₂

• Ca₂O₃

• CaO

• Ca₂O

What is the atomicity of phosphorus in P₄?

• 1

• 2

• 3

• 4

Which of these molecules has the smallest molecular mass?

• H₂O

• CO₂

• CH₄

• N₂

The molar mass of methane (CH₄) is approximately:

• 16 g/mol

• 12 g/mol

• 28 g/mol

• 32 g/mol

In a chemical reaction, the sum of the masses of reactants and products remains constant. This follows the:

• Law of Multiple Proportions

• Law of Conservation of Mass

• Law of Definite Proportions

• Dalton's Atomic Theory

Which of the following elements has the symbol 'Na'?

• Nitrogen

• Neon

• Sodium

• Nickel