Step 1: Concept
Psychotropic substances are chemical agents that affect the mind, emotions, and behavior.
Step 2: Meaning
These are often regulated under strict acts (like the NDPS Act) because they can alter brain function.
Step 3: Analysis
Nifedipine is for blood pressure, Miglitiol is for diabetes, and Chlorthalidone is a diuretic. Glutethimide (often spelled Glutethemine in older texts) is a sedative-hypnotic used for insomnia, which classifies it as a psychotropic drug.
Step 4: Conclusion
Therefore, Glutethemine is the psychotropic substance among the choices.
Final Answer: (B)