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For the second period elements the correct increasing order of first ionisation enthalpy is:
A
Li < Be < B < C < N < O < F < Ne
B
Li < B < Be < C < O < N < F < Ne
C
Li < B < Be < C < N < O < F < Ne
D
Li < Be < B < C < O < N < F < Ne
Detailed Solution
Be ($2s^2$) and N ($2p^3$) have comparatively more stable valence sub-shells than B and O, so their ionisation enthalpies are higher than those of B and O respectively.
Correct order of first ionisation enthalpy: Li < B < Be < C < O < N < F < Ne