Question

Reactions having molecularity $\ge$ 2 and order of reaction $=$ _____ are known as pseudo unimolecular reactions.

Answer 1

Reactions having molecularity $2$ but order of reaction $=1$ are known as pseudo unimolecular reactions.
The inversion of cane-sugar is a first order reaction though its moleculariry is two.

$Sucrose+water\rightleftharpoons Glucose+Fructose$

In this hydrolysis reaction, both sucrose and water participate. Hence, it is a bimolecular reaction.
Since water is present in large excess, its concentration does not appear in the rate law expression.

Hence, the rate law expression is $rate=k\left[sucrose\right]$
Hence, the reaction is first order reaction.
It is called psuedo unimolecular reaction.