Name the part of gynoecium that determines the compatible nature of pollen grain.

Pistil

Explanation: Gynoecium - is the female reproductive part of the flower which is also an essential whorl of the flower, it is made up of pistils.

This pistil has the ability to determine the compatible nature of pollen grain.

The pistil can recognise whether the pollen is compatible (right) or incompatible (wrong).

The pistil accepts the pollen only if the pollen is compatible and then the pistil promotes post-pollination processes leading to fertilisation.

If the pollen is incompatible the pistil rejects the pollen.

Due to continuous communication between pollen and pistil via chemical components of pollens helped pistil to recognise the compatible pollen.