Firstly, Relative Molecular mass = 2 x Vapour Density
The challenge is to find the relative molecular mass = Molar mass of the gas
But we were given V = 560cm3 , Molar Volume = 22.4 dm3 = 22400cm3 and Mass = 0.4g
However, we can obtain the value for Number of moles, then easily obtain the value for our Molar mass, using mass given.
⇒ n = = = 0.025 mole
Also, n =
M = = = 16.0
Recall that Molar mass of gas = 2 x V.D
Therefore, V.D = = 8.0