Which of the following is a crop of Rabi season?

The correct answer is Option (4) → Mustard

Rabi crops are sown in winter, from October to December, and harvested in summer, from April to June. They need cool weather while growing and warmth when ripening. The main rabi crops are wheat, barley, peas, gram and mustard.

The other three are kharif crops, sown with the onset of the monsoon in June-July and harvested in September-October. Maize is mainly a kharif crop, though in some states such as Bihar it is grown in the rabi season as well.