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)H_(3)` is the most stable species because the replacement of H by Br increases positive charge (`-I-`effect) on carbon atom and destabilises the species and, more the number of Br-atoms, less stable is the species.
`overset(Θ)(C)Cl_(3)` is the most stable species because on replacing H by Cl, negative charge on carbon is dispersed due to `-I-`effect of Cl and thus get reduced and species is stabilised. Further, more the number of Cl atoms, more is the dispersal of the negative charge and hence more stable is the species.