Which inorganic precipitate acts as a semipermeable membrane,or what is the chemical composition of a semipermeable membrane?

The osmotic pressure of a $1 \ M$ solution at $27^{\circ}C$ is $(R = 0.082 \ L \ atm \ K^{-1} \ mol^{-1})$: (in $atm$)

The osmotic pressure of a $5\% \ (w/V)$ solution of cane sugar at $150\,^{\circ}C$ will be $.......$ $atm$.

Calculate the amount of solute dissolved in $3 \ dm^3$ water having osmotic pressure $0.3 \ atm$ at $300 \ K$. (Molar mass of solute $= 108 \ g \ mol^{-1}, R = 0.0821 \ atm \ dm^3 \ K^{-1} \ mol^{-1}$) (in $g$)

$3 \ mL$ of solution was made by dissolving $20 \ mg$ of protein at $0^{\circ} C$. The osmotic pressure of the resulting solution is $3.8 \ torr$. The molecular weight of the protein is approximately $(g/mol)$

Which of the following would have the highest osmotic pressure? (Assume that all salts are $90\%$ dissociated.)