Air is pushed into a soap bubble of radius r to double its radius. If the surface tension of the soap solution is S. the work done in the process is  

Number of soap bubble surfaces = 2,
Surface area increase =

$\Rightarrow 4\mathrm{\pi }{\left(2\mathrm{r}\right)}^2-4\mathrm{\pi }{\left(\mathrm{r}\right)}^2 =12{\mathrm{\pi r}}^2$

Surface area total increase = 

$\Rightarrow 2\times 12{\mathrm{\pi r}}^2=24{\mathrm{\pi r}}^2$

Change in surface energy equals work done

$\Rightarrow 5\times 24{\mathrm{\pi }}^2=24{\mathrm{\pi r}}^2\mathrm{s}$

Hence the correct answer is $24{\mathrm{\pi r}}^2\mathrm{s}.$