Which of the following is a day neutral plant?

Correct option is B

The correct answer is (b) Chilli.
Explanation:
A day-neutral plant is a plant that flowers regardless of the length of the day (daylight hours) it receives. Chili peppers (Capsicum spp.) are considered day-neutral plants. They can flower and fruit throughout the year under suitable conditions. 
Why other options are incorrect:
· (a) Onion: Onions are short-day plants. They require a long period of darkness to initiate flowering. 
· (c) Fennel: Fennel is also a short-day plant.
· (d) Capsicum: This is a typo. The correct answer is (b) Chilli, which refers to Capsicum spp.