Assertion: Pollen grains are well preserved as fossils.
Reason: Exine of a pollen grain is made up of sporopollenin which is resistant to high temperatures, strong acids or alkali as well as enzymatic degradation. .

Both assertion(A) and reason (R) are true and reason is the correct explanation of assertion.

The correct answer is Option (2) - Both assertion(A) and reason (R) are true and reason is the correct explanation of assertion.

Pollen grains are generally spherical measuring about 25-50 micrometers in diameter. It has a prominent two-layered wall outer exine and inner intine.

Assertion (A): "Pollen grains are well preserved as fossils." This is true because pollen grains have been found in many fossil records, indicating they are well-preserved over geological timescales.

Reason (R): The hard outer layer called the exine is made up of sporopollenin which is one of the most resistant organic material known. It can withstand high temperatures and strong acids and alkali. No enzyme that degrades sporopollenin is so far known. Pollen grain exine has prominent apertures called germ pores where sporopollenin is absent. Pollen grains are well- preserved as fossils because of the presence of sporopollenin.

Therefore, the reason provided (the composition and properties of sporopollenin) correctly explains why pollen grains are well preserved as fossils.