Question

The vapour densities of two gases are in the ratio of 2:5. their molecular masses are in the ratio of

Answer 1

Alright

Mass = 2*Vapour density
so
M1/M2 = 2*V1 / 2*V2
= 2*2 / 2*5
= 2 / 5

Hope it helped

Answer 2

Vapour density is just half of the molecular weight.

So the ratio of their molecular weights is 4:10 = 2:5 ( the same )