The correct answer is Operation Green Hunt.
Operation Green Hunt is the name that came to be used for the coordinated offensive launched by the central government along with several state governments against Naxalite or Left Wing Extremist groups active in the so called Red Corridor, a belt of forested and tribal regions spanning states like Chhattisgarh, Jharkhand, Odisha, West Bengal, and parts of Andhra Pradesh and Maharashtra. It involved deploying central paramilitary forces such as the CRPF alongside state police to target Naxalite strongholds, particularly from 2009 into 2010 and beyond.
The name itself was popularized by the media and gradually adopted in public discussion to describe this large scale security operation, even though the government at times avoided using the term officially. The other three options, Operation Red Alert, Operation Cobra Den, and Operation Clean Corridor, are not the actual names associated with this anti-Naxalite campaign and do not correspond to any real government operation of that period.
Therefore, the campaign against the Naxalite movement is correctly identified as Operation Green Hunt.