The surface tension and vapour pressure of water at `20^(@)C` is `7.28xx10^(-2)Nm^(-1)` and `2.33xx10^(3)Pa`, respectively. What is the radius of the smallest spherical water droplet which can form without evaporating at `20^(@)C`?

Options

A. `6.25 xx10^(-3)`mm
B. `6.25 xx10^(2)` mm
C. `5xx10^(4)` m
D. `4.5 xx10^(-5)`m

Answer

B

Explanation

The drop will evaporate if the pressure of water is more than the vapour pressure .
Suppose that a water droplet of radius R is formed withput evaporating .
Vapour pressure = Excess pressure in the drop
` = P = (2T)/R` where T is the surface tension
` :. R = (2T)/P = (2xx 7.28 xx10^(-2))/(2.33 xx10^(3))`
` divide 6.25 xx10^(5) m = 6.25 xx10^(-2) ` mm