The compound which is used as an oxidising agent in many chemical industries is:

$(a)$ Study the following chemical equation:
$CaSO_4 \cdot 2H_2O \xrightarrow{373K} CaSO_4 \cdot \frac{1}{2}H_2O + \frac{3}{2}H_2O$
Name the reactant and the product. State one use of the product.

Which metal does not react with acid?

Tap water conducts electricity,whereas distilled water does not. Why?

Answer the following:
$(i)$ Why is Plaster of Paris written as $CaSO_{4} \cdot 1/2 H_{2}O$? How is it possible to have half a water molecule attached to $CaSO_{4}$?
$(ii)$ Why is sodium hydrogen carbonate an essential ingredient in antacids?
$(iii)$ When electricity is passed through an aqueous solution of sodium chloride,three products are obtained. Why is the process called chlor-alkali?

On what basis are acids classified as strong and weak acids?