Explanation

(a)
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \bigtriangleup T_{f} = ik_{f}m\ \ \ \$
$where\ \bigtriangleup T_{f} = depression\ in\ freezing\ point\ \ \ \ \$
i=van,t Hoff factor
m= molality and
and $k_{f}$= freezing point depression constant
For 0.01 molal NaCl solution
$0.37 = 2{\times k}_{f} \times 0.01$
$\therefore$ $\ \ \ \ \ \ \ \ \ \ \ \ \ k_{f} = \frac{0.37}{2 \times 0.01}$ -----(i)
For 0.02 molal urea solution
$\ \ \ \ \ \ \ \ \bigtriangleup T_{f} = 1 \times k_{f} \times 0.02\ \ \ \ \$
$\ \ \therefore{\ \ \ \ \ \ \ k}_{f} = \frac{\bigtriangleup T_{f}}{0.02}$ -----(ii)
From Eqs (i) and (ii)
$\frac{0.37}{2 \times 0.01} = \frac{\bigtriangleup T_{f}}{0.02}\ \$
$\bigtriangleup T_{f} = \frac{0.37 \times 0.02}{2 \times 0.01}\ \ \ \$
$\ \therefore\ \ \ \ \ \ \bigtriangleup T_{f} = {0.37}^{\circ}C$