Question

In which of the following options the order of arrangement does not agree with the variation of property indicated against it?

• A. $B<C<N<O$ (increasing first ionisation enthalpy)
• B. $I<Br<CI<F$ (increasing electron gain enthalpy)
• C. $Li<Na<K<Rb$ (increasing metallic radius)
• D. $A{l}^{3+}<M{g}^{2+}<N{a}^{+}<F^{-}$ (increasing ionic size).

Answer 1

The correct option is C

$Li<Na<K<Rb$ (increasing metallic radius)

For option (a)
First ionisation energy is the energy required to remove an electron from outermost shell.
Hence, correct order is $B<C<O<N$.

For option (b)
Electron gain enthalpy is the energy required to gain an electron in the outermost shell.
Hence, the correct order is $I<Br<F<Cl$.

For option (c)
As we move down the group in alkali metal, metallic radius increases $Li<Na<K<Rb$.

For option (d)
In case of isoelectronic species, as positive charge decreases or negative charge increases the ionic size of the species increases and vice-versa
$A{l}^{3+}<M{g}^{2+}<N{a}^{+}<F^{-}$.