Final answer:
A "paradoxical" effect of nicotine is its ability to induce both stimulation, such as increased concentration, and relaxation, such as mental calmness, in the user simultaneously. Nicotine also suppresses appetite, another paradoxical effect given the stimulating nature of the substance.
Step-by-step explanation:
The "paradoxical" effect of nicotine refers to the simultaneous stimulating and relaxing effects that nicotine has on the user. While nicotine increases arousal and can enhance cognition, which plays a role in increased concentration (option c), it also leads to decreased anxiety and tension, thereby causing mental calmness and relaxation (option b). Additionally, nicotine has been noted to suppress appetite, which is another paradoxical effect given that stimulation is often associated with increased metabolic rates and appetite.
Nicotine is known for its addictive qualities, and it interacts with acetylcholine receptors to affect neurotransmission. The result for most users is an increase in dopamine, which explains the enhanced pleasure and arousal associated with nicotine use. However, nicotine's ability to induce relaxation and calmness appears counterintuitive to these stimulating effects, hence the paradoxical nature. The suppression of appetite is an additional effect that can be seen as paradoxical considering the increased metabolic activity typically associated with stimulants.