3.92 g. of Mohr salt [mol. wt = 392] is present in 100 ml of an aqueous solution. The sulphate ion concentration of the resulting solution is

The chemical formula of Mohr salt is (NH₄​)_2​Fe(SO​₄)_2​.6H₂​O

Concentration=M=$\frac{\mathrm{Wt}.}{\mathrm{Molar} \mathrm{mass}}\times \frac{1000}{\mathrm{V}\left(\mathrm{ml}\right)}=\frac{3.92}{392}\times \frac{1000}{100}=0.1\mathrm{M}$

From the formula of Mohr salt,

we can say that the concentration of sulfate ions =(2×0.1)=0.2M