Question

lonisation energy is highest in

• A. $[Ne]3s^1$
• B. $[Ne]3s^{2}3p^3$
• C. $[Ne]3d^{10},4s^2,4p^3$
• D. $[Ne]3s^{2}3p^4$

Answer 1

Answer: (B)

In a period from left to right ionisation energy of element generally increases and in a group from top to bottom ionisation energy of element decreases.
The ionisation energy of $V$ A group is greater than $VI$ A group due to extra stabilility of half-filled p-subshell.
$[Ne]3s^1$ is present in $IA$ group and third period.
$[Ne]3s^{2}3p^3$ is present in $V$ A group and third period.
$[Ne]3d^{10},4s^{2}4p^3$ is present in $V$ A group and fourth period.
$[Ne]3s^{2}3p^4$ is present in $VI$ A group and third period.
We know that $IE$ of$V$ A group is greater than $VI$ A group.
So, the $IE$ of $[Ne]3s^{2}3p^3$ is greater than $[Ne]3s^{2}3p^4$.
Further,$[Ne]3d^{10}4s^{2}4p^3$ is also placed in $V$ A group but it is placed below the $[Ne]3s^{2}3p^3$.
As the IE in a group from top to bottom decreases therefore, the ionisation energy of $[Ne]3s^{2}3p^3$ is greatest in given elements due to extra stability of half-filled $p$-sub-shell.