A flask containing 12 g of a gas of 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 is the best estimate of the number of molecules left in the flask (`N_(0) =6xx 10^(23) mol^(-1)`)?

Options

A. `6 xx 10^(19)`
B. `6 xx 10^(18)`
C. `6 xx 10^(17)`
D. `6 xx 10^(13)`

Answer

B

Explanation

`P_(1)V_(1)= n_(1)RT_(1)`
`P_(2)V_(2)= n_(2)RT_(2)`
`(n_2)/(n_1)= (P_2)/(P_1) implies n_(2)= 0.1 xx (0.01)/(100)= 10^(-5) mol = 6xx 10^(18)` molecules.