The correct option is B Oxidation and decarboxylation
Ketoglutarate dehydrogenase is an essential enzyme that converts α ketoglutaric acid to succinyl CoA in Krebs' cycle. Such a conversion oxidises the ketoglutaric acid of hydrogen and also removes one CO2. Hence it is a oxidation and decarboxylation reaction. So the answer is 'Oxidation and decarboxylation'.