Assertion: The molecularity of Pseudo-unimolecular reactions is not one but behaves like one.
Reason: Molecularity is defined for both elementary as well as complex reactions.
Answer & explanation
Correct answer: option 3
Molecularity is defined only for elementary reactions and there is no meaning of molecularity for complex reactions.
Those first order reactions whose molecularity is not one but behaves like one are called Pseudo-unimolecular reactions.