Assertion: The stigma is the receptive surface for pollen grains in a flower's carpel.

Reason: The stigma is where pollen grains are produced and stored for future pollination.

The assertion is correct, but the reason is incorrect.

The correct answer is Option (3) - The assertion is correct, but the reason is incorrect.

Explanation:

The assertion states that the stigma is the receptive surface for pollen grains in a flower's carpel. This is correct. The stigma is the part of the carpel that receives pollen during pollination.

The reason provided, "The stigma is where pollen grains are produced and stored for future pollination," is incorrect. Pollen grains are not produced and stored on the stigma. Pollen grains are produced in the anther, which is part of the stamen, not the carpel. The stigma's primary function is to receive pollen grains when they are transferred to it during pollination.

So, while the assertion is correct, the reason is not a valid explanation for it.