An electron tube was sealed off during manufacture at a pressure of `1.2xx10^(-7)` mm of mercury at `27^(@)C.` Its volume is 100 `cm^(3)`. The number of molecules that remain in the tube is

Options

A. `2xx10^(16)`
B. `3xx10^(15)`
C. `3.86xx10^(11)`
D. `5xx10^(11)`

Answer

C

Explanation

For N molecules, `PV=NkT`
`rArrN=(PV)/(kT)=(1.2xx10^(-10)xx13.6xx10^3xx10xx10^(-4))/(1.38xx10^(-23)xx300)`
`rArrN=3.86xx10^(11)`