Taking the vapour density of hydrogen gas as 1. What will be the vapour density of CH4
?

To solve this problem, let's start by understanding what vapour density is. Vapour density is defined as the mass of a certain volume of the gas compared to the mass of the same volume of hydrogen at the same temperature and pressure. It’s mathematically expressed as:

\[ \text{Vapour Density} = \frac{\text{Molar Mass of the Gas}}{\text{Molar Mass of Hydrogen}} \]

Given that the vapour density of hydrogen gas is taken as 1, it means:

\[ \text{Molar Mass of Hydrogen} = 2 \text{ g/mol} \]

Hydrogen gas (H₂) has a molar mass of 2 g/mol.

Now, we need to calculate the vapour density of methane (CH₄). First, find the molar mass of methane:

- Carbon (C) has a molar mass of 12 g/mol.
- Hydrogen (H) has a molar mass of 1 g/mol.

So, the molar mass of CH₄ is:

\[ \text{Molar Mass of CH₄} = 12 + (4 \times 1) = 16 \text{ g/mol} \]

Now, use the vapour density formula:

\[ \text{Vapour Density of CH₄} = \frac{\text{Molar Mass of CH₄}}{\text{Molar Mass of Hydrogen}} \]
\[ \text{Vapour Density of CH₄} = \frac{16 \text{ g/mol}}{2 \text{ g/mol}} \]
\[ \text{Vapour Density of CH₄} = 8 \]

So, the vapour density of methane (CH₄) is 8.