Correct Answer: Appropriate

Solution : The correct choice is the fourth option.

The word that is opposite in meaning to "incongruous" among the provided options is "appropriate."

The term "incongruous" refers to something that is out of place or inconsistent. On the other hand, "appropriate" suggests that something is suitable or fitting for a particular situation. While "incongruous" implies a lack of harmony or inconsistency, "appropriate" signifies correctness and suitability.

The meanings of the other options are as follows:

Unharmonious refers to a lack of harmony or agreement, indicating a discordant or incompatible state.

Jarring describes something that produces a harsh, unpleasant, or incongruous effect, often causing a disturbance or shock.

Fettered means to be restrained or confined.

Therefore, the correct antonym is appropriate.