1. Solution and colligative properties — Chemistry STD 12 Science — Question

Moles of $\left[\mathrm{Na}^{+}\right]$ ions $=0.2 \times 0.5=0.1$

Concentration of $\left[\mathrm{Na}^{+}\right]$ ions $=\frac{0.1}{2}=0.05 \,\mathrm{M}$

Moles of $\left[\mathrm{Mg}^{2+}\right]$ ions $=0.4 \times 1.5=0.6$

Concentration of $\left[\mathrm{Mg}^{2+}\right]$ ions

$=\frac{0.6}{2}=0.3\, \mathrm{M}=7.2\, \mathrm{gm} / \mathrm{L}$

Moles of $\left[\mathrm{Cl}^{-}\right]$ ions $=0.2 \times 0.5+2 \times 0.4 \times 1.5$

                                $=1.3$

Concentration of $[\mathrm{Cl}^-]$ ions $=\frac{1.3}{2}=0.65\, \mathrm{M}$