Explanation:

- Deficiency refers to the lack or shortage of something necessary.

- Option 1: Abundance means a large quantity or plenty of something. It is the opposite of deficiency.

- Option 2: Sufficiency signifies an adequate amount of something, which is more neutral compared to deficiency.

- Option 3: Inadequacy means insufficient or lacking, which aligns with the concept of deficiency.

- Correct Answer: Option 3: Inadequacy

- Option 4: Efficiency indicates the ability to achieve a goal with minimal waste, which does not relate directly to the concept of lacking or deficiency.