Assertion (A): The Himalayan soils are rich in humus. Reason (R): The Himalayas have the largest area under forest cover
In Assertion-Reason, check both parts calmly. Here, the combination that fits is (A) is false, but (R) is true. In Soil, this is how Assertion and Reason are linked. If you check Assertion first, then Reason, then the link, the answer becomes clear. That is the simple way to do it.
Ref: [UP Lower Sub. (Spl)(Pre) 2004] | Majid Husain, Geography of India, and NCERT Geography textbooks discuss Soil and explain the Indian geographical features and patterns that support the correct answer for this question.