The number of lone pairs on chlorine atom in ${\text{ClO}}^{-}{\text{,\hspace{0.17em}ClO}}_{\text{2}}^{-}{\text{,\hspace{0.17em}ClO}}_{\text{3}}^{-}{\text{,\hspace{0.17em}ClO}}_{\text{4}}^{-}$ ions respectively are

In all of the oxoacids of chlorine, chlorine undergoes sp³ hybridization$\begin{array}{l}{\text{ClO}}^{-}-\text{1\hspace{0.17em}bond\hspace{0.17em}pair,\hspace{0.17em}3\hspace{0.17em}lone\hspace{0.17em}pairs}\\ {\text{ClO}}_2^{-}-\text{2\hspace{0.17em}bond\hspace{0.17em}pairs,\hspace{0.17em}2\hspace{0.17em}lone\hspace{0.17em}pairs}\\ {\text{ClO}}_3^{-}-\text{3\hspace{0.17em}bond\hspace{0.17em}pairs,\hspace{0.17em}1\hspace{0.17em}lone\hspace{0.17em}pair}\\ {\text{ClO}}_4^{-}-\text{4\hspace{0.17em}bond\hspace{0.17em}pairs,\hspace{0.17em}0\hspace{0.17em}lone\hspace{0.17em}pair}\end{array}$