Among the following, the correct order of acidity is:

1. $\mathrm{H}\mathrm{C}\mathrm{l}{\mathrm{O}}_3<\mathrm{H}\mathrm{C}\mathrm{l}{\mathrm{O}}_4<\mathrm{H}\mathrm{C}\mathrm{l}{\mathrm{O}}_2<\mathrm{H}\mathrm{C}\mathrm{l}\mathrm{O}$
2. $\mathrm{H}\mathrm{C}\mathrm{l}\mathrm{O}<\mathrm{H}\mathrm{C}\mathrm{l}{\mathrm{O}}_2<\mathrm{H}\mathrm{C}\mathrm{l}{\mathrm{O}}_3<\mathrm{H}\mathrm{C}\mathrm{l}{\mathrm{O}}_4$
3. $\mathrm{H}\mathrm{C}\mathrm{l}{\mathrm{O}}_2<\mathrm{H}\mathrm{C}\mathrm{l}\mathrm{O}<\mathrm{H}\mathrm{C}\mathrm{l}{\mathrm{O}}_3<\mathrm{H}\mathrm{C}\mathrm{l}{\mathrm{O}}_4$
4. $\mathrm{H}\mathrm{C}\mathrm{l}{\mathrm{O}}_4<\mathrm{H}\mathrm{C}\mathrm{l}{\mathrm{O}}_2<\mathrm{H}\mathrm{C}\mathrm{l}\mathrm{O}<\mathrm{H}\mathrm{C}\mathrm{l}{\mathrm{O}}_3$

Solution

Acidic strength $\propto$ stability of conjugate base (Anion)
stability of conjugate base $\propto$ less charge density $\propto$ more charge delocalisation$\propto$ resonating structure

Oxidation state of chlorine $\propto$ Acidity of Oxo Acid.
$\mathrm{H}\mathrm{C}\mathrm{l}\mathrm{O}<\mathrm{H}\mathrm{C}\mathrm{l}{\mathrm{O}}_2<\mathrm{H}\mathrm{C}\mathrm{l}{\mathrm{O}}_3<\mathrm{H}\mathrm{C}\mathrm{l}{\mathrm{O}}_4$ is the correct increasing order.

Asked in: NEET 2016 (Phase 1)

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