Question

Addition of a non-volatile solute to a solvent always increases the colligative property such as $\pi ,\frac{\Delta P}{P^{\circ }},\Delta T_b$ and $\Delta T_f$. All these colligative properties are directly proportional to the molality. The increase in colligative properties is due to increase in number of solute particles.
For different aqueous solutions of 0.1 N urea, 0.1 N NaCl, 0.1 N $N{a}_{2}S{O}_4$ and 0.1 N $N{a}_{3}P{O}_4$ solutions at ${27}^{\circ }C$, the correct statements are:
(I) The order of osmotic pressure is $NaCl>N{a}_{2}S{O}_4>N{a}_{3}P{O}_4>Urea$
(II) $\pi =\frac{\Delta T_b}{K_b}RT$ for urea solution
(III) Addition of salt on ice increases its melting point
(IV) Addition of salt brings melting of ice earlier

• A. (II), (III), (IV)
• B. (I), (II), (IV)
• C. (I), (II), (III)
• D. (III), (IV)

Answer 1

The correct option is B (I), (II), (IV)

Molar concentrations are
0.1 M urea, 0.1 M NaCl,$\frac{0.1}{2}N{a}_{2}S{O}_4$ and $\frac{0.1}{3}N{a}_{3}P{O}_4$
$\therefore$ From $\pi$ = iCRT (I) is correct
$\Delta T_b=i{K}_{b}m$
Since for dilute solutions, molarity = molality
$\therefore$ (II) is also correct
And addition of salt lowers the freezing point
$\therefore$ (III) is incorrect and (IV) is correct