Which of the following concentrations of solutions of urea in water exhibits minimum freezing point depression?

Calculate van't Hoff factor for aqueous solution of 0.02 m formic acid if it freezes at -0.045 $^\circ\text{C}$.
[ $K_f$ = 1.86 K kg $\text{mol}^{-1}$ and freezing point of water = $0\ ^\circ\text{C}$ ]

Calculate the molar mass of nonvolatile solute when 4 g of it is dissolved in 100 g solvent that boils at 319.4 K [$K_b$ = 2.4 K kg $\text{mol}^{-1}$; B.P of pure solvent = 319 K]

If the emf of cell, $\text{Cu}_{(s)} \mid \text{Cu}^{2+}_{(1M)} \| \text{Ag}^{+}_{(1M)} \mid \text{Ag}$ is 0.463 V at $25\ ^\circ\text{C}$ and standard potential of Cu electrode is 0.337 V. Find the standard potential of Ag electrode