Which one can act as a semipermeable membrane?

$A$ graph of osmotic pressure $(\pi)$ vs molarity $(M)$ of an aqueous solution of $NaCl$ at room temperature is given below. The slope of the line represents :-

$A$ solution contains a non-volatile solute of molecular mass $M_p$. Which of the following can be used to calculate the molecular mass of the solute in terms of osmotic pressure ($m = \text{Mass of solute}$,$V = \text{Volume of solution}$,and $\pi = \text{Osmotic pressure}$)?

When does the osmotic pressure of a solution increase?

If the osmotic pressure of a solution at $300 \ K$ is $0.0821 \ atm$,what will be the concentration of the solution in $mol/L$?

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