Which of the following always indicates that a physical change has taken place ? a) rusting b) burning c) melting d) changing color

The correct answer option is C) Melting.

Explanation:

Physical changes can be defined as the changes which affect the form of a chemical substance but not its chemical composition. These are the changes in which no bonds are broken or formed.

Melting is a physical change. Taking an example of melting ice: water simply changes its physical state but its chemical composition is same for both Ice and liquid water.

t = 1/400 h   ⇔ 0.0025 h ⇔ 9s ⇔ 0.15 m

any of the answers are correct.