Question

Chloride ion and potassium ion are isoelectronic. Then :

• A. Their sizes are same
• B. $C{l}^{-}$ions is bigger than $K^{+}$ion
• C. $K^{+}$ion is relatively bigger
• D. Their sizes depend on other cation and anion

Answer 1

Answer: (B)

Both $K^{+}$and $C{l}^{-}$are isoelectronic each having 18 electrons but each of them differ in their nuclear charge. $K^{+}$has $+19$ nuclear charge whereas $C{l}^{\prime }$ has $+17$ nuclear charge. Thus $K^{+}$ has shorter radius than $C{l}^{-}$because in case of $K^{+}$due to increased nuclear charge, electrostatic attractions also increases which results in shorter radius.
Thus option $B$ is correct. $C{l}^{-}$ion is bigger than $K^{+}$ion.