Given the elementary reaction: a + 2b → ab₂, what is the molecularity of this reaction?

• A. Bimolecular
• B. Termolecular
• C. Tetramolecular
• D. Unimolecular

Answer: (B)

Verified step by step guidance

1. Understand that molecularity refers to the number of reactant particles (molecules, atoms, or ions) involved in a single elementary reaction step.
2. Identify the reactants and their stoichiometric coefficients in the given elementary reaction: a + 2b → ab₂.
3. Count the total number of reactant molecules involved in the elementary step. Here, there is 1 molecule of 'a' and 2 molecules of 'b', so the total is 1 + 2 = 3 molecules.
4. Recognize that since three reactant molecules collide simultaneously in this elementary step, the molecularity is three, which is called termolecular.
5. Conclude that the molecularity of the reaction a + 2b → ab₂ is termolecular because it involves three reactant molecules colliding in a single step.