Question

Ionization energy is highest in _______.

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

Answer 1

The correct option is B $\left[Ne\right]3s^{2}3p^3$

$\left[Ne\right]3s^{2}3p^3$ has the highest ionisation energy because along the period ionisation energy increases (as effective nuclear charge increases).

It has a half-filled 3p sublevel which is more stable than a partially filled sublevel in $\left[Ne\right]3s^{2}3p^4$, sulphur. This is why phosphorus has higher first ionization energy than sulphur.

Hence, option B is correct.