Question

Th increasing order of the first ionization enthalpy of the elements $B,P,S$ and $F$ is:

• A. $B<P<S<F$
• B. $B<S<P<F$
• C. $F<S<P<B$
• D. $P<S<B<F$

Answer 1

The correct option is B $B<S<P<F$

$B$ and $F$ lies in the second period while $P$ and $S$ lies in the third period. Because of higher effective nuclear charge, first ionization energy of $P$ and $F$ are higher than that of $B$ and $S$ . Among $P$ and $S$, $P$ has higher first ionization energy due to exactly half filled configuration of $P$.
Again, effective nuclear charge increases as we move from left to right in the periodic table. Thus $F$ has the highest first ionization energy value and $B$ has the least value of first ionization energy.
$\therefore$ Overall increasing order of first ionization energy is $B<S<P<F$.
i.e., (b) is correct.