The correct order of acid character of the following compounds is :

$\mathrm{II}>\mathrm{III}>\mathrm{IV}>\mathrm{I}$

$\mathrm{III}>\mathrm{II}>\mathrm{I}>\mathrm{IV}$

$I V>I I I>I I>I$

$\mathrm{I}>\mathrm{II}>\mathrm{III}>\mathrm{IV}$