The expression relating molality (m) and mole fraction of solute $(x_2)$ in a solution is (where $M_1$ is the molar mass of solvent)

Question

$\begin{array}{1 1}x_2=\large\frac{mM_1}{1+mM_1}\\x_2=\large\frac{mM_1}{1-mM_1}\\x_2=\large\frac{1+mM_1}{mM_1}\\x_2=\large\frac{1-mM_1}{mM_1}\end{array} $