Refer to the below reaction:

Question

 

The epoxidation reaction is

$\begin{array}{1 1}a)\;bimolecular\; nucleophilic\; addition\\b)\;Unimolecular\; nucleophillic\; addition\\c)\;Unimolecular\; electrophillic\; addition\\d)\;Bimolecular\; electrophillic \;addition\end{array}$