Step 1: Meaning of "Ardent"
The word ardent means intensely passionate, eager, or enthusiastic about something. It conveys strong emotional involvement and zeal.
Step 2: Check each option
- (a) Indifferent: means having no particular interest or concern; apathetic. This is the opposite of passionate. ✔
- (b) Zealous: means full of zeal, strongly devoted, or enthusiastic. This is actually a synonym, not an opposite. ✘
- (c) Fervent: means showing passionate intensity, again a synonym of ardent. ✘
- (d) Enthusiastic: means excited or keen interest. This is again a synonym. ✘
Step 3: Conclusion
The only word that is the exact opposite of Ardent is Indifferent.
\[
\boxed{\text{Answer = (a) Indifferent}}
\]