a. Explain why the second ionisation energy of `B` is significantly higher than the second ionisation energy of `C`, even though the first ionisation energy of `B` is less than `C`.
b. which has higher `1st` ionisation energy `B` or `Be` and why?

Explanation

a. `B_(5)1s^(2)2s^(2)2p^(1)`,`C(6)1s^(2)2s^(2)2p^(2)`
`B` after losing one electron, has completely filled `s`-orbital from which removal of electron is more difficult than carbon.
b. Be has higher first ionisation energy due to completely filled valence `s`-orbital.