Final answer:
The correct speed control for an EKG tracing of a patient with a heart rate of 150/min is 25 mm/sec, as it provides optimal spacing for analysis without overlap or excessive spread of the EKG complexes.
Step-by-step explanation:
An EKG technician is preparing to perform a 12-lead EKG tracing on a patient with a heart rate of 150/min. The appropriate paper speed to best capture the data is 25 mm/sec. At a higher speed, such as 50 mm/sec, the tracing may be too spread out, while at lower speeds, such as 5 mm/sec or 10 mm/sec, the EKG tracings could overlap, making accurate diagnosis difficult. Therefore, the 25 mm/sec speed allows for optimal spacing of the EKG complexes on the tracing at a high heart rate, facilitating a clearer analysis of the heart's rhythm and electrical activity.