According to Graham's law of diffusion, the rates of diffusion of two gases are inversely proportional to square root of their densities.
Thus, we have
rH/r0 = √{ρ0/ρH}
As the box contains equal no. of hydrogen and oxygen molecules,
ρ0/ρH > 1 ⇒ rH = r0
i.e., hydrogen will leak out rapidly