A tube of fine bore `AB` is connected to a manomeer `M` as shown. The stop cock `S` controls the flow in air. `AB` is dipped into a liquid whosw surface tension is `sigma`. On opening the stop cock for a while, a bubble is formed at `B` and the manometer level is recorded, showing a difference `h` in the levels in the two arms. If `rho` be the density of manometer liquid and `r` the radius of curvature of the bubble, then the surface tension `sigma` of the liquid is given by
A. `rhohrg`
B. `2rhohrg`
C. `4rhohrg`
D. `(rhrhog)/4`
