2nd ionisation potential of Be is greater than the 1st ionisation potential of B but less than 2nd ionisation potential of B - explain .

Explanation

For first ionisation of boron `(1s^(2) 2s^(2) 2p^(1))` one electron is to be removed from the singly filled 2p-orbital and this requires lesser energy , while for second ionisation of `Be(1s^(2) 2s^(1))` one electron is to be removed from the more penetrating singly filled 2 s -orbital . So , second ionisation potential of Be is greater than the first ionisation potential of B . On the other hand , for second ionisation potential of boron `(1s^(2) 2s^(2))` , one electron is to be removed from completely filled 2s-orbital . This causes the second ionisation potential of Be to be lesser than the second ionisation potential of B .