For a non-volatile solute in a volatile solvent: $P_{solution}$ = $x_{solvent}$ * P_{solvent}_{standard}. RLVP: $\frac{P_standard - P_solution}{P_standard}$ = $\frac{delta_P}{P_standard}$ = $x_{solute}$ = $\frac{n_solute}{n_solute + n_solvent}$. For dilute solutions: $delta_P$/$P_{standard}$ ≈ $n_{solute}$/$n_{solvent}$ = $\frac{w_solute/M_solute}{(w_solvent/M_solvent)}$. This is used to find molar mass of non-volatile solutes. For electrolytes: $delta_P$/$P_{standard}$ = i * $x_{solute}$. Important: RLVP applies only when the solute is non-volatile. If both components are volatile (like benzene + toluene), use Raoult's law for both — RLVP formula does not apply directly.