Question

Strongest conjugate base is :

• A. $Cl{O}^{-}$
• B. $Cl{O}_2^{-}$
• C. $Cl{O}_3^{-}$
• D. $Cl{O}_4^{-}$

Answer 1

Answer: (A)

$Cl{O}^{-}$

If acid is weak, its conjugate base is strong.
Greater the oxidation number of Cl, stronger the acid and thus, weaker the conjugate base.
Acid oxidation no of Cl conjugate base
$HClO$ +1 $Cl{O}^{-}$
$HCl{O}_2$ +3 $Cl{O}_2^{-}$
$HCl{O}_3$ +5 $Cl{O}_3^{-}$
$HCl{O}_4$ +7 $Cl{O}_4^{-}$
As we move down the group, strength of acid increases while strength of base decreases, so strongest base is $Cl{O}^{-}$.