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^(15)`

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 = `6 xx 10^(18)` molecules