Question

it has been observed that brightness after the whitewashing appears after one or two day by support your observation by giving suitable chemical reaction
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Answer 1

Answer:

First, Calcium oxide is added to water to form Calcium Hydroxide.

⇒  $CaO + H_{2}O$ ⇒ $Ca(OH)_{2}$

Then, it is applied to walls, where it is exposed to Carbon dioxide to form Calcium Carbonate.

⇒  $Ca(OH)_{2} + CO_{2}$ ⇒ $CaCO_{3}$

It takes time for the water to evaporate from the walls. That is the reason why the bright white colour of  $CaCO_{3}$  takes atleast a day or two to appear.