Transfer of pollen grains from anther of one flower to the stigma of a flower of different plant is called as:

Xenogamy

The correct answer is Option (3) → Xenogamy

The transfer of pollen grains from the anther of one flower to the stigma of a flower of a different plant is called xenogamy.

Xenogamy is the process of cross-pollination between two different plants of the same species, leading to greater genetic diversity. It involves the transfer of pollen from the flower of one plant to the flower of another plant.

The other terms are defined as follows:

• Fertilization: The fusion of male and female gametes to form a zygote, which occurs after pollination.
• Geitonogamy: The transfer of pollen from the anther of one flower to the stigma of another flower on the same plant, which is technically a form of self-pollination.
• Cleistogamy: A type of self-pollination that occurs in closed flowers that do not open, ensuring that pollination happens within the same flower.

So, the correct answer is: Xenogamy.