Particle Nature of Matter: Molecules MCQs Quiz | Class 9

Class IX Science (Code 086) Unit I: Matter – Its Nature and Behaviour. This quiz covers the Particle Nature of Matter: Molecules, focusing on the molecule concept and types at the element and compound level. Attempt the 10 MCQs below to test your understanding, then submit to check your score and download the answer key PDF.

Overview of Molecules

A molecule is the smallest particle of an element or a compound that is capable of an independent existence and shows all the properties of that substance. Atoms of the same element or of different elements can join together to form molecules.

Molecules of Elements vs. Compounds

  • Molecules of Elements: These are constituted by the same type of atoms. For example, Argon (Ar) and Helium (He) consist of only one atom. Oxygen (O2) consists of two atoms.
  • Molecules of Compounds: Atoms of different elements join together in definite proportions to form molecules of compounds. For example, water (H2O) contains Hydrogen and Oxygen combined in a ratio of 1:8 by mass.

Atomicity

The number of atoms constituting a molecule is known as its atomicity.

Type Name Atomicity
Non-Metal Argon Monoatomic
Non-Metal Oxygen Diatomic
Non-Metal Phosphorus Tetra-atomic
Non-Metal Sulphur Poly-atomic

Quick Revision Points

  • Atoms in a molecule are held together by attractive forces called chemical bonds.
  • Noble gases like Helium and Neon are monoatomic.
  • Metals generally do not form simple molecules; they exist as large aggregates of atoms (e.g., Iron, Copper).
  • The chemical formula represents the composition of a molecule.

Extra Practice Questions

  1. Define atomicity with an example.
  2. Why are noble gases called monoatomic?
  3. Calculate the ratio by mass of atoms present in Ammonia (NH3).
  4. Differentiate between a molecule of an element and a molecule of a compound.
  5. Name a tetra-atomic molecule of a non-metal.