Which from following mixtures exhibits positive deviation from Raoult's law?

Calculate the osmotic pressure of 0.5 M aqueous solution of nonvolatile solute at 300 K .

$$ \left[\mathrm{R}=0.0821 \mathrm{~atm} \mathrm{dm} \mathrm{~K}^{-1} \mathrm{~mol}^{-1}\right] $$

Calculate the number of moles of nonvolatile solute dissolved in 0.3 kg solvent if $\Delta \mathrm{T}_{\mathrm{b}}=0.3 \mathrm{~K}$ and $\mathrm{K}_{\mathrm{b}}$ for solvent is $1.8 \mathrm{~K} \mathrm{~kg} \mathrm{~mol}^{-1}$.

Calculate the boiling point elevation of solution if 15 g urea is dissolved in 1000 g water. $\left[\mathrm{K}_{\mathrm{b}}\right.$ for water $=0.52 \mathrm{~K} \mathrm{~kg} \mathrm{~mol}^{-1}$; molar mass of urea $=60 \mathrm{~g} \mathrm{~mol}^{-1}$ ]