Match the following non-dimensional numbers with the corresponding definitions:

$\begin{array}{|c|c|c|cI|} \hline {} & \textbf{Non-dimensional number} & {} & \textbf{Definition} \\ \hline \textbf{P} & \text{Reynolds number} & \textbf{1} & \dfrac{\text{Buoyancy force}}{\text{Viscous force}} \\ \\ \hline \textbf{Q} & \text{Grashof number} & \textbf{2} & \dfrac{\text{Momentum diffusivity}}{\text{Thermal diffusivity}} \\ \\ \hline \textbf{R} & \text{Nusselt number} & \textbf{3} & \dfrac{\text{Inertia force}}{\text{Viscous force}} \\ \\ \hline \textbf{S} & \text{Prandtl number} & \textbf{4} & \dfrac{\text{Convective heat transfer}}{\text{Conduction heat transfer}} \\ \\ \hline \end{array}$

1. $P-1, Q-3, R-2, S-4$
2. $P-3, Q-1, R-2, S-4$
3. $P-4, Q-3, R-1, S-2$
4. $P-3, Q-1, R-4, S-2$