T is surface tension
${\rm{P in air bubble }} = {{\rm{P}}_0} + \rho g{\rm{gh}} + \frac{{2\;{\rm{T}}}}{{\rm{R}}}$
${{\rm{P}}_{{\rm{in }}}} - {{\rm{P}}_0} = \rho g\;{\rm{g}} + \frac{{2\;{\rm{T}}}}{{\rm{R}}} = 2100$
$\frac{{2\;{\rm{T}}}}{{\rm{R}}} = 2100 - \rho {\rm{gh}}$
$\;{\rm{T}} = \frac{{\rm{R}}}{2}\left( {2100 - {{10}^3} \times 10 \times 0.2} \right)$
$ = \frac{1}{{20}}(2100 -2000) \times {10^{ - 2}}$
$ = 0.05$