Question

The number of atoms present in one molecule of an elementary substance is called its:
(A) Atomicity
(B) Valency
(C) Molecular Weight
(D) Isotopic index

Answer 1

Hint: Try to understand the different terms mentioned in the options given above. Write an example for each term. This will help you to clearly identify as well as find common ground with the question mentioned above.

Complete step by step solution:
-The sum of all atomic masses of all atoms present in the molecule is called its molecular weight. Molecular weight can be measured in different scales like grams, atomic mass units etc. However, the magnitude of mass will remain the same as it is independent of the scale used.
-Valency is the measure of the combining capacity of an atom or molecule with another atom/molecule. It denotes the number of electrons a particular atom can gain or lose to participate in a chemical reaction.
-Isotopic index indicates the number of neutrons in excess to the starting isotope of an element.
-Atomicity is defined as the total number of atoms present or that constitute a molecule. For example, the atomic of an oxygen molecule is 2 as there are two oxygen atoms present.
From the above explanation of the terms mentioned in options, we can conclude that the number of atoms present in one molecule of an elementary substance is known as atomicity.

Therefore, the correct answer is option (A).

Note: In older contexts, the term atomicity was often considered synonymous or similar to the term valency of an atom/molecule. However, they are not to be considered the same. The explanation for each term has already been discussed in the solution part.