Question

Which of the following is/are wrong order(s)?

• A. $B^{+}<B<B^{-}\text{Size}$
• B. $I<Br<Cl<F-\text{Electron gain enthalpy}$
• C. $O^{--}<O^{-}<O^{+}{\text{Z}}_{\text{eff}}$
• D. $Na<Al<Mg<Si\text{Ionisation potential}$

Answer 1

The correct option is B $I<Br<Cl<F-\text{Electron gain enthalpy}$

Consider the factors on which these properties depend:
(A) Cation is smaller while anion is bigger than its parent atom. correct order is $B^{+}<B<B^{-}$
(B) Correct order of electron gain enthalpy is $Cl>F>Br>I$
(C) Cation is smaller as it is formed by the loss of electron(s). The anion is formed by the gain of electron(s). The size of anion increases with increase in charge on anion i.e.. as the $Z/e$ ratio decreases the size increases.
(D) Across the period the size decreases and nuclear size increases. So, ionisation energy increases. However, the first ionisation energy of $Mg$ is greater than $Al$ because of high penetration power of $2s^2$ electrons of $Mg$ as compared to that of $2p^1$ electron of $Al$.
hence, $Na<Al<Mg<Si$ is the order of Ionisation potential.