Question

A chemical reaction is often accompanied by external indications or characteristics which include – 

1. Colour change
2. Effervescence or gas evolved
3. Evolution or absorption of heat
4. Formation of a precipitate.

With reference to each of the above indications, state the external indication seen during – Addition of dilute acid to an active metal.

Answer 1

Addition of dil. acid to an active metal: Gas is evolved, test tube or flask becomes hot (heat is produced).