Question

A change in which the chemical composition of a substance remains the same are known as :

Answer 1

Based on chemical composition, changes can be of two types-

1. Chemical Changes
2. Physical Changes

Chemical change	Physical change
It is a permanent change and can not be reversed back.	These are temporary changes and can be reversed back.
Change in chemical composition of a substance takes place.	No change in chemical composition of a substance takes place.
New substance is formed.	No new substance is formed.
For example- Conversion of milk to curd, Rusting etc. $\underset{\mathrm{Iron}}{\mathrm{Fe}\left(\mathrm{s}\right)}+\underset{\mathrm{Water}}{\mathrm{x}.\mathrm{H}2\mathrm{O}\left(\mathrm{l}\right)}\to \underset{\mathrm{Hydrated}\mathrm{Iron}\mathrm{oxide}\left(\mathrm{Rust}\right)}{\mathrm{Fe}2\mathrm{O}3.\mathrm{xH}2\mathrm{O}\left(\mathrm{s}\right)}$	For example, Melting of ice to water. After melting of ice, chemical composition of water still remains the same i.e H2O .

Hence, Composition of matter remains same in a physical change.