Question

Vapour density of methane is
(A) 8
(B) 16
(C) 4
(D) 2

Answer 1

Hint :The density of a vapour in comparison to hydrogen is known as vapour density. It may be calculated by dividing the mass of a particular volume of a material by the mass of the same volume of hydrogen. 2 vapour density = molar mass. The density of vapour is a unitless number.

Complete Step By Step Answer:
A gas or vapor relative weight in comparison to air, which has an arbitrary value of one. If the vapour density of a gas is less than one, it will rise in air. When the vapour density exceeds one, the gas will sink in the air. The mass of a molecule is measured in daltons and is called molecular mass (m) (Da or u). The molecular mass and relative molecular mass are not the same as the molar mass, but they are linked. The molar mass is stated in g/mol and is defined as the mass of a particular substance divided by the quantity of that substance. When dealing with macroscopic (weighable) amounts of a material, the molar mass is typically the more suitable figure.
The most official definition of molecular weight is that it is identical with molecular mass; nevertheless, it is also extremely changeable in practise, as are the units used in combination with it. Many common preparation sources use g/mol as a shorthand for molar mass, but more reputable sources use Da or u and define it more closely with the molecular mass.
The ratio of the mass of one molecule of a material to the mass of 1/12th of a carbon atom, or 1 amu, is known as relative molecular mass. The ratio of the mass of a volume of a gas to the mass of an equivalent amount of hydrogen, measured at the same temperature and pressure, is known as vapour density.
Molecular mass of methane = 16
Hence since, 2 Vapour density = Molecular mass
2 x VD = 16
VD = 8
Vapour density of methane is 8.
Option (A) is correct.

Note :
Even when the units Da or u are used, the molecular weight is often expressed as a weighted average, comparable to the molar mass but with different units. The weight of macromolecules is referred to as their molecular weight in molecular biology, and it is measured in kDa.