The correct answer is option 4, which means that the Assertion (A) is false and the Reason (R) is true.

The Assertion (A) statement is incorrect because when tropical rain forests are cleared, the land does not remain productive for several years without chemical fertilizers. Tropical soils are generally poor in nutrients and when a rainforest is cleared, essential nutrients stored in the vegetation are lost quickly due to heavy rains and the soil is exhausted within a few years.

On the other hand, the Reason (R) statement is accurate as the primary productivity, which is the rate at which plants and other photosynthetic organisms produce organic compounds in an ecosystem, is indeed very high in tropical rainforests compared to temperate forests. This is because tropical rainforests have a longer growing season and a higher level of sunlight, both of which enhance photosynthesis and result in higher primary productivity.

Hence, while both statements are about tropical rainforests, the Reason (R) does not provide a correct explanation for the Assertion (A), making option 4 the accurate choice.