An air bubble of radius 0.1 cm lies at a depth of 20 cm below the free surface of a liquid of density 1000 kg / m^3. If the pressure inside the…

An air bubble of radius $\displaystyle 0.1$ cm lies at a depth of $\displaystyle 20$ cm below the free surface of a liquid of density $\displaystyle 1000 \mathrm{~kg} / \mathrm{m}^3$. If the pressure inside the bubble is $\displaystyle 2100 \mathrm{~N} / \mathrm{m}^2$ greater than the atmospheric pressure, then the surface tension of the liquid in SI unit is (use $\displaystyle \mathrm{g}=10 \mathrm{~m} / \mathrm{s}^2$ )