The volume of hydrogen is 200 mL.
Graham's law of effusion states that the rate of effusion of a gas is inversely proportional to the square root of the mass of its molecules.
We can write the formula as
#color(blue)(bar(ul(|color(white)(a/a) r_2/r_1 = sqrt(M_1/M_2)color(white)(a/a)|)))" "#
If gas 2 is hydrogen and gas 1 is oxygen, then
Hydrogen diffuses 3.984 times as fast as oxygen, so the original volume of oxygen must be