The correct option is C Assertion is correct but Reason is incorrect
The molecularity of a reaction is a whole number other than zero, but generally less than 3
Order may be zero or fractional or whole number or negative..
Thus, reactions can be classified as unimolecular, bimolecular etc. Molecularity is less than 3 because, it is difficult to obtain effective collisions between 3 or more molecules.
Thus, Assertion is correct but Reason is incorrect.