If 280cm3 of hydrogen diffuses in 40secs, how long will it take for 490cm3 of a gas x, whose vapor density is 25 to diffuse under the same condition (RMM hydrogen =2)

The time taken by gas x : 350 s

Graham's law: the rate of effusion of a gas is inversely proportional to the square root of its molar masses or  

the effusion rates of two gases = the square root of the inverse of their molar masses:  

Molar mass = 2 x vapour density(VD)

r₁=rate Hydrogen = 280 cm³ / 40 s = 7 cm³/s

M₁=molar mass Hydrogen=2 g/mol

M₂=molar mass gas x=

i belive it is water

5.6⋅10−^19  j

do you need the explaination?