Question

Find the total number of elements given below, which have higher ionisation energy than their both adjacent elements (in a period).
$Be,B,N,P,C,S,Mg$

Answer 1

The adjacent element of $Be$ is $Li$ and $B$.
Ionization energy of $Be$ is greater than that of $Li$ because as we move from left to right ionization energy increases due to increase in effective nuclear charge.
Ionisation energy of $Be$ is greater than that of $B$ because of completely filled electronic configuration of $Be$.

The adjacent element of $N$ are $C$ and $O$.
Ionization energy of $N$ is greater than that of $C$ because as we move from left to right ionization energy increases due to increase in effective nuclear charge.
Ionisation energy of $N$ is greater than that of $O$ because of half filled electronic configuration of $N$.

The adjacent element of $P$ are $Si$ and $S$.
Ionization energy of $P$ is greater than that of $Si$ because, as we move from left to right ionization energy increases due to increase in effective nuclear charge.
Ionisation energy of $P$ is greater than that of $S$ because of half filled electronic configuration of $P$.

The adjacent element of $Mg$ are $Na$ and $Al$.
Ionization energy of $Mg$ is greater than that of $Na$ because as we move from left to right ionization energy increases due to increase in effective nuclear charge.
Ionisation energy of $Mg$ is greater than that of $Al$ because of completely filled electronic configuration of $Mg$.