Which one of the following is dimensionless?
1
\(\frac{\partial p}{\partial x}\cdot \frac{D^4}{\mu Q^2}\)
2
\(\frac{\partial p}{\partial x}\cdot \frac{D^3}{\mu Q}\)
3
\(\frac{\partial p}{\partial x}\cdot \frac{D^4}{\mu Q}\)
4
\(\frac{\partial p}{\partial x}\cdot \frac{\mu Q}{D^4}\)