Question

Element having highest I.P. among the following is:

• A. $H$
• B. $Li$
• C. $B$
• D. $Na$

Answer 1

The correct option is C $B$

${}_{1}H=1s^1$

${}_{3}Li=1s^{2}2s^1$

${}_{5}B=1s^{2}2s^{2}2p^1$

${}_{11}Na=1s^{2}2s^{2}2p^{6}3s^1$

Ionisation potential of $B$ will be highest as when we move from $Li⟶B$ size decreases thereby increasing effective nuclear charge. Also the last $e^{-}$ is added in the $2p$ orbital of $B$. Hence requires more energy as it is more near to the nucleus than $3s$.