Correct Answer: Productive

Solution : The correct answer is the first option .

The adjective vain describes someone who has an excessively high opinion of his appearance, abilities, or worth.

Its antonym is the adjective productive. It refers to achieving or producing significant results, often associated with efficiency and accomplishment.

The meanings of the other options are as follows:

The noun harmony means an agreement or accord; a state of peaceful coexistence.

The adjective unpredictable means being unpredictable, uncertain, or subject to variation.

The adjective calculable describes something that can be calculated or estimated and exhibits predictability.

Therefore, the correct antonym is productive.