The expression relating molarity (M) and molality (m) of a solution is (where $\rho$ is the density of solution and $M_2$ is the molar mass of solute)

Question

$\begin{array}{1 1}m=\large\frac{M}{\rho+MM_2}\\m=\large\frac{M}{\rho-MM_2}\\m=\large\frac{\rho+MM_2}{M}\\m=\large\frac{\rho-MM_2}{M_2}\end{array} $