Atoms and Molecules

Who proposed the atomic theory?

• J.J. Thomson

• John Dalton

• Ernest Rutherford

• Niels Bohr

What is the smallest unit of an element that retains its chemical properties?

• Molecule

• Compound

• Atom

• Ion

Which law states that mass can neither be created nor destroyed in a chemical reaction?

• Law of Constant Proportions

• Law of Conservation of Mass

• Law of Multiple Proportions

• Avogadro’s Law

Which law states that in a chemical substance, the elements are always present in definite proportions by mass?

• Law of Conservation of Mass

• Law of Definite Proportions

• Law of Multiple Proportions

• Law of Variable Proportions

What is the molecular formula of water?

• H₂

• H₂O

• O₂

• HO₂

How many atoms are there in one molecule of carbon dioxide (CO₂)?

• 1

• 2

• 3

• 4

Which unit is used to express atomic mass?

• Gram

• Kilogram

• Atomic Mass Unit (amu)

• Mole

What is the valency of an element?

• The number of protons in the nucleus

• The number of neutrons in the nucleus

• The combining capacity of an element

• The number of electrons in the outermost shell

What is the mass of one mole of a substance called?

• Atomic mass

• Molecular mass

• Molar mass

• Formula mass

Which of the following is a polyatomic ion?

• Na⁺

• Cl⁻

• SO₄²⁻

• H⁺