Correct Answer: Antagonistic

Solution : The correct option will be the third option.

The most appropriate synonym for the given word opposite is antagonistic.

Antagonistic refers to something that is opposed or hostile. In the context of opposite, which denotes being contrary or diametrically different, "antagonistic" is the most appropriate synonym.

The meanings of the other options are:

Noticeable: It means easily seen or observed; attracting attention.

Conspicuous: It means easily visible, attracting attention through being unusual or remarkable.

Similar: It means having a resemblance in appearance, character, or quantity without being identical.

Therefore, the correct answer will be antagonistic.