Write any two observations in an activity which may suggest that a chemical reaction has taken place. Give an example in support of your answer.

(i) Formation of gaseous compound or element and effervescence of the same.

Example:

Zn (s) + 2HCl (aq.) ZnCl₂ (aq.) + H₂ (g)

Here Hydrogen gas is released.

(ii) Precipitate formation.

Example: Adding potassium iodide in a solution of lead nitrate, the yellow color precipitate(lead-iodide) is formed.