Question

The number of molecules involved in a molecular reaction is called:

• A. Molecularity
• B. Order of reaction
• C. Unimolecular reaction
• D. Rate of reaction

Hint:

Molecularity refers only to elementary reactions and is always a positive integer such as 1, 2, or 3.

Answer 1

The Correct Option is A

Concept: Chemical reactions occur when atoms, ions, or molecules collide with one another. The number of reacting particles that participate simultaneously in an elementary reaction is known as molecularity.

Step 1: Understand molecularity.
Molecularity tells us how many molecules are involved in a single elementary reaction step. Examples: \[ A \rightarrow Products \] This involves one molecule and is called a unimolecular reaction. \[ A+B \rightarrow Products \] This involves two molecules and is called a bimolecular reaction. \[ A+B+C \rightarrow Products \] This involves three molecules and is called a termolecular reaction.

Step 2: Distinguish molecularity from order.
Many students confuse molecularity with order of reaction.

• Molecularity is a theoretical quantity.

• It is always a positive whole number.

• Order of reaction is determined experimentally.

• Order can be zero, fractional, or even negative.

Step 3: Identify the correct term.
Since the question asks for the number of molecules participating in a reaction, the required term is: \[ \boxed{\text{Molecularity}} \]