Solution A contains $7 g /L$ of ${\mathrm{MgCl}}_2$ and solution B contains $7 g/L$of $\mathrm{NaCl}$. At room temperature, the osmotic pressure of

 

${\mathrm{MgCl}}_2\rightleftharpoons {\mathrm{Mg}}^{2+}+2{\mathrm{Cl}}^{-}\text{i.e., }1+2=3$ particles

$\mathrm{NaCl}\rightleftharpoons {\mathrm{Na}}^{+}+{\mathrm{Cl}}^{-}\text{i.e., }1+1=2$ particles

Osmotic pressure is a colligative property which depends upon the number of particles. The number of

particles in ${\mathrm{MgCl}}_2$ being more than that in $\mathrm{NaCl}, {\mathrm{MgCl}}_2$

solution will have higher osmotic pressure