Correct Answer: Efficiency

Solution : The correct answer is the second option.

In the given context, "efficacy" refers to the ability to produce the desired or intended result, indicating effectiveness. "Efficiency" serves as an appropriate synonym in this context because it also conveys the idea of achieving optimal results with minimal wasted resources.

The meanings of the other options are as follows:

Impotence: This term refers to the lack of power or effectiveness, opposite to the intended meaning of efficacy.

Ineptness: This term suggests incompetence and contrasts with the effectiveness implied by efficacy, indicating a lack of skill or ability.

Futility: Futility refers to the lack of practical significance or the pointlessness of an action, which is the opposite of achieving the desired result implied by efficacy.

Therefore, the correct answer is efficiency.