In a venturi meter. $\Delta P_{1}$ and $\Delta P_{2}$ are the pressure drops corresponding to volumetric flowrates $Q_{1}$ and $Q_{2}$. If $Q_{2}/Q_{1}=2$, then $\Delta P_{2}/\Delta P_{1}$ equals
1. $2$
2. $4$
3. $0.5$
4. $0.25$