Final answer:
The offset of effects of a bolus of propofol is caused by redistribution. Hence, option B is correct.
Step-by-step explanation:
The process responsible for the offset of effects of a bolus of propofol is redistribution. Propofol is a short-acting anesthetic that is rapidly distributed throughout the body, including the central nervous system, after administration. As the drug is redistributed from the site of action, its effects diminish.