Account for the following:

(i) $N{F}_{3}$ is an exothermic compound but $NC{I}_{3}$ is an endothermic compound.

(ii) HF is not stored in glass bottles but is kept in wax-coated bottles.

(iii) Bleaching of flowers by $C{l}_{2}$ is permanent while that of $S{O}_{2}$ is temporary.