The surface tension for pure water in a  capillary tube experiment is

• A

  $\frac{\mathrm{\rho g}}{2\mathrm{hr}}$

• B

  $\frac{2}{\mathrm{hr\rho g}}$

• C

  $\frac{\mathrm{r\rho g}}{2\mathrm{h}}$

• D

  $\frac{\mathrm{hr\rho g}}{2}$