Match the instruments in $Group\; I$ with their corresponding measurements in $Group\; II$.

$$\begin{array}&&\textbf{Group I} & \textbf{Group II} \\ &\text{P. Manometer} & \text{1. Agitator speed}\\ &\text{Q. Rotameter} & \text{2. Pressure difference} \\ &\text{R. Tachometer} & \text{3. Cell number} \\ &\text{S. Haemocytometer} & \text{4. Air flow rate} \\ \end{array}$$

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