Question

In which of the following pairs, the ionization energy of the first species is less than that of the second:

• A. $O^{-},O^{2-}$
• B. $S,P$
• C. $N,P$
• D. $B{e}^{+},Be$

Answer 1

Answer: (B)

$S,P$

Variation in the period among the representative elements:

Ionisation energies generally increase along the period because in moving left to right in a period the effective nuclear charge per outermost electron increases while the corresponding principal quantum number remains same.

However, due to half-filled configuration, $P$ has higher IP than $S.$