Question

Which of the following has highest ionisation energy?

• A. $k^{+}$
• B. $C{l}^{-}$
• C. $Ar$
• D. $C{s}^{+}$

Answer 1

Answer: (A)

Ionisation energy increases with decrease in size of atoms or ions.
$\underset{C{s}^{+}Cl<Ar<K^{+}}{\overset{\text{Increase in ionisation energy}}{\to }}$
Since, $K^{+}$ has the smallest size, therefore, it has the highest ionisation energy among the given.