For the second period elements the correct increasing order of first ionisation enthalpy is:

General trend: Ionisation Enthalpy increases from left to right.
Exceptions:

Be>B: Be (2s
2
) has a stable fully-filled subshell, whereas B (2s
2
2p
1
) has one electron in 2p which is easier to remove.

N>O: N (2p
3
) has a stable half-filled p-subshell, whereas O (2p
4
) has one paired electron in 2p experiencing more repulsion.
Correct order: Li