How many plants in the list given below have unisexual flowers?Castor, maize, pea, papaya, wheat, rice, Vallisneria, tomato, brinjal, gram, bean.

The correct option is D Five
A flower is a reproductive structure found in flowering plants. A unisexual flower possesses either stamens or carpels but not both. A plant may be unisexual (dioecious), possessing only male flowers or female flowers; or it may be monoecious with male and female reproductive organs borne in the same flower or in different unisexual flowers but on the same plant. Plants like maize, castor, pea, papaya, Vallisneria have either male or female flowers, or flowers present as different flowers but in the same plant.

So the correct option is 'five'.