Explanation:

- Authentic means genuine or real. It describes something that is true to its origins.

- Option 1: Authoritative relates to being trusted or commanding. It's more about having authority or credibility.

- Option 2: Baseless means without foundation or evidence. It suggests something false or lacking proof.

- Option 3: Ridiculous means deserving mockery or being absurd. It doesn’t accurately oppose authenticity.

- Option 4: Vacuous means lacking thought or intelligence. It's about emptiness, not fakeness.

The nearest antonym to "authentic" is option 2: Baseless because something baseless lacks the genuineness inherent in authenticity.

Baseless