At STP, 22.4 L of any gas = 1 mol moles of the gas = 5.6/22.4 = 0.25 moles Since, molar mass = mass of 1 mole = 4 x mass of 0.25 moles Hence, molar mass of the gas = 4 x 8 g (mass of 0.25 moles) = 32 g Now we know that ,  Molecular mass= 2 x vapour density  Hence vapour density = molecular mass/2 = 32/2 = 16

Given Information:
- Volume of gas (V) = 5.6 litres
- Weight of gas (W) = 8 grams

To find:
- Vapour density of the gas

Definition of Vapour Density:
Vapour density is defined as the ratio of the mass of a given volume of a substance to the mass of an equal volume of a standard substance, usually hydrogen or air.

Formula:
Vapour density (D) = (W × M) / (V × m)
- W: Weight of the gas
- V: Volume of the gas
- M: Molar mass of the gas
- m: Molar mass of the standard substance (usually air)

Step-by-Step Solution:

Step 1: Determine the molar mass of the gas.
- Molar mass (M) is the mass of one mole of a substance.
- The molar mass of the gas can be determined using the periodic table or other sources.

Step 2: Determine the molar mass of the standard substance (usually air).
- The molar mass of air is approximately 28.97 grams/mol.

Step 3: Substitute the given values into the formula to calculate the vapour density.
- Vapour density (D) = (8 g × M) / (5.6 L × 28.97 g/mol)

Step 4: Simplify the equation and calculate the vapour density.
- The units of grams cancel out, leaving the vapour density in g/L.
- Perform the calculation to find the value of vapour density.

Explanation:
The vapour density of a gas is a measure of its relative density compared to a standard substance, which is usually air or hydrogen. It provides information about the molecular mass and composition of the gas.

By using the given volume and weight of the gas, along with the molar mass of the gas and the standard substance, we can calculate the vapour density using the formula mentioned above.

The molar mass of the gas is necessary to determine the ratio of the mass of the gas to the mass of an equal volume of the standard substance. The molar mass can be obtained from the periodic table or other sources.

The molar mass of the standard substance, usually air, is known to be approximately 28.97 grams/mol. This value is used in the formula as the molar mass of the standard substance.

By substituting the given values into the formula and performing the calculation, we can find the vapour density of the gas. The units of grams cancel out, leaving the vapour density in g/L.

It is important to note that the vapour density of a gas is a relative value and does not have any units. It provides a comparison between the density of the gas and the density of the standard substance.

In conclusion, the vapour density of the gas can be calculated using the given information and the formula mentioned above. Make sure to substitute the correct values and units to obtain an accurate result.