Question 1

Which of the following is a physical change?

Accepted Answer

A physical change is a reversible change in which no new substance is formed. Melting of wax is a physical change because only the state of matter changes from solid to liquid, and it can be solidified back into wax without changing its chemical composition.

Question 2

Which of the following represents a chemical change?

Accepted Answer

Rusting of iron is a chemical change because a new substance (iron oxide) is formed, and the change is generally irreversible under normal conditions.

Question 3

Cutting a log of wood into pieces is a:

Accepted Answer

Cutting a log of wood into pieces is a physical change because only the size and shape of the wood change, and no new chemical substance is formed.

Question 4

Formation of clouds is an example of:

Accepted Answer

Formation of clouds involves the condensation of water vapor, which is a physical change because water changes its state from gas to liquid without altering its chemical identity.

Question 5

The chemical name of rust is:

Accepted Answer

Rust is chemically known as hydrated iron oxide (Fe2O3.xH2O), which is formed when iron reacts with oxygen and moisture present in the air.

Physical and Chemical Changes — CBSE Class 7 Science Important Questions & Revision Notes