Identify the most stable species in the following set of ions giving reasons
(a) `overset(+)(C)H_(3), overset(+)(C)H_(2) Br, overset(+)(C)HBr_(2), overset(+)(C)Br_(3)` (b) `overset(Θ)(C)H_(3), overset(Θ)(C)H_(2)Cl, overset(Θ)(C)HCl_(2), overset(Θ)(C)Cl_(3)`

Explanation

(a) `overset(-) C-Cl_3` is most stable because `Cl` is more electronegative than hydrogen. On replacing hydrogen by chlorine, negative charge on C is reduced and the species becomes stable.
(b) `overset(+) CH_3` is most stable. The replacement of H by Br increases positive charge on carbon atom because Br is more electronegative than H and consequently the species becomes less stable.