Dr. Smith is curious about ways to improve worker productivity. She believes that employees with harsher work environments might actually be more productive, because they are less relaxed and more driven. She gets permission from a sales company to conduct a research study, and she splits the company’s employees into two groups by having people pull a piece of paper out of a hat – each piece of paper has either "bright" or "dim" written on it. The people in the "bright" group have their lighting replaced with harsh, bright light bulbs, and the people in the "dim" group have their lighting replaced with soft, pleasant light bulbs. She then measures their productivity over a 4-week period, and finds that the people in the "harsh" group actually make more sales than the people in the "dim" group.

Which of the following represents the operational dependent variable?

a. worker productivity
b. number of sales made
c. harshness of work environment
d. type of lighting (bright or dim)

Productivity seems to be a measure including its effectiveness of transforming inputs towards usable outputs of an individual, plant, manufacturer, or perhaps a device.
Job efficiency seems to be a dependent variable here. The Dependent variable would be what the investigator tests during an investigation. Here, by adjusting independent factors, the investigator tests job efficiency.

All other decisions taken are also not connected to the example in the case offered. So, the solution above is indeed the right one.