$($a$)$

How many molecules are present in a sample of an ideal gas that occupies a volume of $1\mathrm{.}40$ cm$3,$ is at a temperature of $20$C$,$ and is at atmospheric pressure?

molecules

$($b$)$

How many molecules of the gas are present if the volume and temperature are the same as in part $($a$),$ but the pressure is now $2\mathrm{.}901011$ Pa $($an extremely good vacuum$)?$

molecules