van't Hoff factor

Consider separate solutions of 0.500 M $\ce{C2H5OH(aq)}$, 0.100 M $\ce{Mg3(PO4)2(aq)}$, 0.250 M $\ce{KBr(aq)}$ and 0.125 M $\ce{Na3PO4(aq)}$ at 25°C. Which statement is true about these solutions, assuming all salts to be strong electrolytes ?

The observed osmotic pressure for a 0.10 M solution of $\ce{Fe(NH4)2(SO4)2}$ at 25°C is 10.8 atm. The expected and experimental (observed) values of Van't Hoff factor (i) will be respectively :

(R = 0.082 L atm k$^{-1}$ mol$^{-1}$)

The freezing point (in °C) of a solution containing 0.1 g of $\ce{K3[Fe(CN)6]}$ (Mol. Wt. 329) in 100 g of water ($K_f=1.86$ K kg mol$^{-1}$) is

When 20 g of naphthoic acid ($\ce{C11H8O2}$) is dissolved in 50 g of benzene ($K_f=1.72$ K kg mol⁻¹), a freezing point depression of 2 K is observed. The van't Hoff factor ($i$) is