Give reasons for the following.
a. LiCI is more covalent than KCI.
b. LiI has lower melting point than LiF.
c. During electrolysis of molten sodium chloride, calcium chloride and potassium fluoride are added.

Explanation

a. `Li^(o+)` ion has smaller size as compared to `K^(o+)` ion and thus `Li^(o+)` ion is more polarising as compered to `K^(o+)` ion and hence LiCI is more convalent than KCI.
b. `F^(Θ)` ion has smaller size as compared to `I^(Θ)` ion, therefore `F^(Θ)` ion is less polarisable as compered to `I^(Θ)` ion and hence LiF is less convalent than LiI.
Thus LiI has lower melting point than LiF.
c. Pure sodium has a very high melting point `(1074 K)`. During electrolysis. `CI_(2)` gas is evolved which has corrosive action on the cell at high temperatures. Further, the cost of electricity to attain and maintain this temperature is very high. Therefore,to lower the fusion temperature to about `850-875` K, `CaCI_(2)` and KF are added to molten NaCI.