Question

The vapour density of a certain gas X is 4 times that of Y. The molecular mass of X is M the molecular mass of Y is
a)4M
b)0.5M
c)0.25M
d)0.33M

Answer 1

Molecular mass = 2×vapour density

From this relation,

Your answer is (c).

Answer 2

We know that vapour density of any gas = molecular mass divided by the mass of Hydrogen gas (2)

or vapour density = half of the molecular mass


Then as given

vapour density of X = 4 times vapour density of Y

Mass of X = M

Vapour density of X = M/2 = 0.5 M

now from above

0.5M = 4Y

=> Y = 0.125M

or vapour density of Y = 0.125 M

therefore mass of Y = 0.125M× 2
= 0.250 M
or 0.25 M


Answer = option "c"


Hope it helps you