Question

Chloride ion and potassium ion are isoelectronic. Then :

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