A flask containing `12 g` of a gas relative molecular mass `120 at` a pressure of `100 atm` was evacuated by means of a pump until the pressure was `0.01 atm`. Which of the following in the best estimate of the number of molecules left in the flask `(N_(0)=6xx10^(23)mol^(-1))`?

Explanation

Initially, `n_(1)=(12)/(120)` mole=0.1 mole, `P_(1)`=100 atm, `T_(1)`=T, `V_(1)`=V
After evacuation, `n_(2)`=? `P_(2)=0.01`atm, `T_(2)=T, V_(2)=V`
Applying PV=nRT
As V and T an constant, `(P_(1))/(P_(2))=(n_(1))/(n_(2))`
`(100)/(0.01)=(0.1)/(n_(2))" or "n_(2)=(0.1xx0.01)/(100)=(10^(-1)xx10^(-2))/(10^(2))=10^(-5)` mole
No. of molecules left `=(10^(-5))(6.02xx10^(23))=6.02xx10^(18)`