A drop of liquid pressed between two glass plates spreads to a circle of diameter 10cm. Thickness of liquid film is 0.5mm and coefficient of surface tension is $70\times {10}^{-3}{\mathrm{Nm}}^{-}$. The force required to pull them a part is

The formula for the force caused by surface tension is $\mathrm{F}=\mathrm{T}l$, where l is the length of contact.
Here, $l=2\mathrm{\pi r}$, resulting in force on a single plate.

$\mathrm{F}=\mathrm{T}\times \mathrm{L}=2\mathrm{T}\times \frac{\mathrm{A}}{\mathrm{d}}$

$\mathrm{F}=\frac{2\times 70\times {10}^{-3}\times \mathrm{\pi }\times (5\times {10}^{-2})}{0.5\times {10}^{-3}}$

$\mathrm{F}=4\times 70\times \mathrm{\pi }\times 25\times {10}^{-4}=2198\times {10}^{-3}=2.2\mathrm{N}$

Hence the correct answer is 2.2N.