The electronic structure of four elements `A,B, C, D` are
(a) `1s^(2)` (b) `1s^(2), 2s^(2), 2p^(2)`
( c) `1s^(2), 2s^(2), 2p^(5)` (d) `1s^(2), 2s^(2) 2p^(6)`
The tendency to form electrovalent bond is largest in