Unisexuality of flower prevents which type of pollination?

Autogamy but not geitonogamy.

The correct answer is Option (3) – Autogamy but not geitonogamy.

Unisexuality of flower refers to the presence of either male or female reproductive organs in a flower. This means that a unisexual flower cannot self-pollinate, which is called autogamy. However, it can still be pollinated by pollen from another flower of the same plant, which is called geitonogamy.

Xenogamy is pollination between flowers of different plants. This can still occur in unisexual flowers, as long as the pollen from the male flower is transferred to the stigma of a female flower of a different plant.

Therefore, unisexuality of flower prevents autogamy but not geitonogamy.

The other options are incorrect. Xenogamy is not prevented by unisexuality of flower, because the pollen can still be transferred from a male flower to a female flower of a different plant. Geitonogamy is not prevented by unisexuality of flower, because the pollen can still be transferred from a male flower to a female flower of the same plant. Autogamy is prevented by unisexuality of flower, because there are no male and female reproductive organs in the same flower.