Final answer:
A nurse should use an electronic blood pressure measurement device for an infant in the pediatric unit because it is more suitable for their small arm and the difficulty of manual measurements in this age group.
Step-by-step explanation:
The client on whom a nurse should perform an electronic blood pressure measurement is C. An infant in the pediatric unit. When measuring the blood pressure of an infant, it is important to use an electronic blood pressure device that is appropriately sized for the infant's small arm, as manual measurement can be challenging and less accurate in this age group. Adults with hypertension or hypotension and pregnant women can typically be assessed using a manual sphygmomanometer, which allows for auscultatory measurements that can provide more accurate readings in the presence of factors like arrhythmias or pulsus paradoxus that might impact electronic devices' accuracy.