Give reason:
a. `CaCI_(2)` is added to NaCI in the electrolytic manufacture of sodium.
b. An aqueous solution of iodine becomes colourless, on adding excess of sodium hydroxide.

Explanation

a. Pure sodium chloride melts at about `800^(@)C`. At this temperature, both sodiumand chloride (products of electrolysis) are corrosive in nature. Sodium also forms metallic fog at this temperature. To remove these problems, the fusion temperature is reduced to `600^(@)C` by adding `CaCI_(2)`.
b. Sodium reacts with NaOH forming colourless compounds. Thus the colour of iodine disppears on adding NaOH.
`NaOH+I_(2)rarr underset("Collourless products")ubraceunderset("iodide hypoiodite")underset("Sodium Sodium")(NaI+NaIO)+H_(2)O`