Step 1: Understanding the Concept:

The word ’nocturnal’ refers to animals or plants that are active, blooming, or happening during the night. An antonym is a word that has the exact opposite meaning.

Step 2: Detailed Explanation:

1. Nocturnal: Active at night.

2. Normal: Usual, typical, or expected. Not an antonym of time-of-day activity.

3. Diurnal: Active during the day. This is the direct biological and linguistic opposite of nocturnal.

4. Abnormal: Deviating from what is normal or usual.

5. Exceptional: Unusual; not typical.

Step 3: Final Answer: Since nocturnal means ”of the night” and diurnal means ”of the day”, option (B) is the correct antonym.