Question

Atomicity of the oxygen molecule is ______
A. 2
B. 3
C. 4
D. 5

Answer 1

Hint: Recall the definition of atomicity along with the molecular mass and atomic mass of oxygen. Atomicity is the number of atoms present in a homonuclear molecule. It can also be found by dividing the molecular weight by the atomic weight.

Complete step by step solution:
Atomicity is defined as the number of atoms of a substance that are present in a molecule of the same substance. It is defined only in homonuclear molecules. According to whether the molecules are monatomic, diatomic, or triatomic, the atomicity can be 1, 2, or 3 respectively. This is one way to calculate atomicity. Some polyatomic molecules also exist that have atomicities like 4 and 8.
Another way is to consider the atomic mass of the element along with the molecular mass of the element when it is found naturally. Then divide the molecular mass by the atomic mass and you will get the atomicity.
Atomicity of the same element can be different for different allotropes found naturally. Elements like carbon, silicon and metals which form large unending change are said to have atomicity 1 for the sake of convenience.
We know that oxygen is a diatomic molecule. Its molecular mass is 32 and atomic mass is 16.
\[\text{Atomicity = }\dfrac{\text{Molecular mass}}{\text{Atomic mass}}\]
\[Atomicity=\dfrac{32}{16}\]
Atomicity = 2
Hence, the answer is ‘A. 2’

Additional information:
Atomicity of commonly found elements:

Element	Atomicity
Carbon	1
Nitrogen	2
Sulphur	8
Phosphorous	4
Helium	1
Fluorine	2
Iron	1
Copper	1

Note: Do not get confused between the terms atomicity and valency. Atomicity concerns only the number of atoms present in a molecule. Valency involves the number of electrons that can be exchanged or shared.