For Problem 1:
I assume you are asking for the volume back on Earth at STP (1 bar and 0 °C).
We can use the Combined Gas Laws equation.
#color(blue)(|bar(ul(color(white)(a/a) (P_1V_1)/T_1= (P_2V_2)/T_2color(white)(a/a)|)))" "#
We can rearrange the Combined Gas Laws equation to get
There are twice as many dinitrogen molecules as dioxygen molecules.
So, dinitrogen is two-thirds of the total number of molecules and generates two-thirds of the total pressure.
Dinitrogen exerts two-thirds of 1686 torr, i.e. 1124 torr.