The formation of a gas in a chemical reaction, due to ions changing places, often indicates that the reaction is which type?

Explanation:

A chemical reaction is defined as a reaction which leads to change in chemical composition of a substance.

During a chemical change there might be evolution of gas which is an indication that composition of reactants has been changed.

For example, precipitation, combustion etc causes chemical changes.

On the other hand, a change which does not cause any change in chemical composition of the substance is known as a physical change.

For example, size, volume, mass etc are physical changes.

Thus, we can conclude that formation of a gas in a chemical reaction, due to ions changing places, often indicates that the reaction is chemical change.