Question

Identify the correct statement:

• A. Molecularity of a reaction is an experimental quantity.
• B. For complex reactions molecularity has no meaning.
• C. Molecularity of a reaction can be zero or even a fraction.
• D. Molecularity more than three is very common in chemical reactions.

Hint:

Molecularity is always a whole number and applies only to elementary reactions. If a reaction is complex (multi-step), molecularity is not defined.

Answer 1

The Correct Option is B

Concept: Molecularity is defined as the number of reacting species (atoms, ions, or molecules) that collide simultaneously in an elementary step of a reaction. Key properties:

• It is defined only for
  elementary reactions.
• It is always a
  positive integer (1, 2, or rarely 3).
• It is a
  theoretical concept, not experimentally determined.
• It has
  no meaning for complex (multi-step) reactions.

Step 1: Check each statement.
Option (A): Molecularity is not an experimental quantity. It is derived from the reaction mechanism. Hence, incorrect.
Option (B): Complex reactions occur in multiple elementary steps, and molecularity is defined only for individual elementary steps. Thus, for complex reactions, molecularity has no meaning. Hence, correct.
Option (C): Molecularity cannot be zero or fractional. It must be a whole number. Hence, incorrect.
Option (D): Reactions with molecularity greater than 3 are extremely rare because simultaneous collision of many particles is unlikely. Hence, incorrect.