Explanation

(d)
There are two different reactants (say A and B).
$A + B \rightarrow product\$
Thus, it is a bimolecular reaction .
If $\frac{dx}{dt} = k\lbrack A\rbrack\lbrack B\rbrack$
It is second order reaction
If ($\frac{dx}{dt}) = k\lbrack A\rbrack$
Or =k[B]
It is first order reaction .
Molecularity is independent of rate ,but is the sum of the reacting substance thus it cannot be unimolecular reaction .