Correct Answer: Option B

Explanation

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 = 560cm\(^3\) , Molar Volume = 22.4 dm\(^3\) = 22400cm\(^3\) 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 = \(\frac{V}{M.V}\) = \(\frac{560}{22400}\) = 0.025 mole

     Also, n  =  \(\frac{m}{M}\) 

             M = \(\frac{m}{n}\) = \(\frac{0.4}{0.025}\) = 16.0

Recall that Molar mass of gas = 2 x V.D

Therefore, V.D = \(\frac{16.0}{2}\) = 8.0

There is an explanation video available below.

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