Which of the following is the increasing order of $P^H$ of 0.1M solution of the compounds
 (A)${\mathrm{HCOONH}}_4$  (B) ${\mathrm{CH}}_3{\mathrm{COONH}}_4$  (C)${\mathrm{CH}}_3\mathrm{COONa}$  and (D) ${\mathrm{NH}}_4\mathrm{Cl}$ is correct.

${\mathrm{HCOONH}}_4\rightleftharpoons \underset{\mathrm{WA}}{{\mathrm{HCOO}}^{-}}+\underset{\mathrm{WB}}{{\mathrm{NH}}_4^{+}}$

${\mathrm{CH}}_3{\mathrm{COONH}}_4\leftrightharpoons \underset{\mathrm{WA}}{{\mathrm{CH}}_3{\mathrm{COO}}^{-}}+\underset{\mathrm{WB}}{{\mathrm{NH}}_4^{+}}$

${\mathrm{CH}}_3\mathrm{COONa}\leftrightharpoons \underset{\mathrm{WA}}{{\mathrm{CH}}_3{\mathrm{COO}}^{-}}+\underset{\mathrm{SB}}{{\mathrm{Na}}^{+}}$

${\mathrm{NH}}_4\mathrm{Cl}\rightleftharpoons \underset{\mathrm{WB}}{{\mathrm{NH}}_4^{+}}+\underset{\mathrm{SA}}{{\mathrm{Cl}}^{-}}$

$\Rightarrow$The increasing order of pH

$\Rightarrow$${\mathrm{NH}}_4\mathrm{Cl}$<${\mathrm{HCOONH}}_4$<${\mathrm{CH}}_3{\mathrm{COONH}}_4$<${\mathrm{CH}}_3\mathrm{COONa}$

$\mathrm{HCOOH}$ is a stronger acid that of ${\mathrm{CH}}_3\mathrm{COOH}$

Hence, ${\left({\mathrm{pK}}_{\mathrm{a}}\right)}_{\mathrm{HCOOH}}<{\left({\mathrm{pK}}_{\mathrm{a}}\right)}_{{\mathrm{CH}}_3\mathrm{COOH}}$

Where WB$\Rightarrow$Weak Base, SB$\Rightarrow$Strong Base, WA$\Rightarrow$Weak Acid, SA$\Rightarrow$Strong Acid