C

Schedule X of the Indian Drugs & Cosmetics Rules lists habit-forming/psychotropic agents such as amphetamines, methaqualone – and ketamine – that require special licence and triplicate prescriptions; the other choices (thalidomide, colistin, halothane) fall under different schedules or none at all. Ketamine is therefore the only Schedule X drug among the options [Rohrig, 2010, PMID 20077083].