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.
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