Why the first ionisation energy of carbon atom is greater than that of boron atom whereas, the reverse is true for the second ionisation energy.

Answer

[Zeff & half filled config.]

Explanation

`[C = 1s^(2) 2s^(2) 2p^(2)`
`B = 1s^(2) 2s^(2) 2p^(1)`
Left to right atomic size decreases, `IE_(1) uarr` After the removal of `1e^(-), B` acquire fully filled stable s-orbital configuration, therefore `IE_(2)` of `B gt C`