Antonym of FACTITIOUS

ridiculous
genuine
engineered
magnificent

The correct answer is B. Genuine.

A factitious thing is not genuine or real. It is made up or artificial. A genuine thing is real and not made up. It is authentic.

The other options are not antonyms of factitious.

A ridiculous thing is very silly or absurd. It is not to be taken seriously.

An engineered thing is designed and built by humans. It is not natural.

A magnificent thing is very impressive or grand. It is not ordinary or common.