Question

The correct order of increasing first ionisation enthalpy is:

• A. $Li<Be<B<C$
• B. $Li>Be>B>C$
• C. $Li<Be>B<C$
• D. $Li<B<Be>C$
• E. $Li>Be<B<C$

Answer 1

The correct option is C $Li<Be>B<C$

Atom	before ionization	After ionization
Li	$1S^{2}2S^1$	$1S^2$
Be	$2S^2$	$2S^1$
B	$2S^{2}2P^1$	$2S^2$
C	$2S^{2}2P^2$	$2S^{2}2P^1$

Ionization enthalpy-The ionization energy is qualitatively defined as the minimum amount of energy required to remove the most loosely bound electron, the valence electron of an isolated neutral gaseous atom.

As we move from left to right in any period, the ionization enthalpy increases due to an increase in the nuclear charge.

Thus, the order should be $Li<Be<B<C$,

But, the $Be$ has full-filled electronic configuration whereas $B$ does not.

Thus, $Be$ will have more ionization energy than $B$.

Thus the correct order of ionization enthalpy is:

$Li<Be>B<C$