$(R = 0.083 \,L\, bar \,mol^{-1}\, K{-1})$
$2.57 \times 10^{-3} \times \frac{200}{1000}=\frac{1.26}{m} \times 0.083 \times 300$
$m=61039\; \mathrm{gm} \mathrm{mol}^{-1}$
(આપેલ, $K_f = 5\,K\, kg\,mol^{-1},$ બેન્ઝોઇક એસિડનું મોલર દળ $= 122\,g\,mol^{-1}$ )