The bacteria involved in the reduction of the nitrate ion (NO3) to nitrogen dioxide (NO2), di-nitrogen oxide (N2O), nitrogen monoxide (NO) or nitrogen (N2) is
Nitrobacter
Pseudomonas denitrificans
Nitrosomonas
Azotobacter
The bacteria involved in the reduction of the nitrate ion (NO3) to nitrogen dioxide (NO2), di-nitrogen oxide (N2O), nitrogen monoxide (NO) or nitrogen (N2) is Pseudomonas denitrificans. Hence, the correct answer is option b.