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Arrange the following elements in increasing order of first ionization enthalpy:
$Li$, $Be$, $B$, $C$, $N$
Choose the correct answer from options given below:
A
Li < Be < C < B < N
B
Li < Be < N < B < C
C
Li < Be < B < C < N
D
Li < B < Be < C < N
Detailed Solution
Across period 2, atomic size decreases and effective nuclear charge increases, so ionisation enthalpy generally increases.
Exception: Be ($2s^2$, fully filled 2s) has a higher ionisation enthalpy than B ($2s^22p^1$), whose single 2p electron is removed easily.
(N, with half-filled $2p^3$, has a higher value than C.)
Correct order: Li < B < Be < C < N