Explanations:The main crop of mountain soil is tea and coffee. This is because mountainous regions, such as those found in Assam, have specific climatic and soil conditions that are highly suitable for these crops. Mountain soil is characterized by its high organic content, which results from the decomposition of organic matter in the cooler, more humid environment. This type of soil is well-drained and rich in nutrients, which are essential for the growth of tea and coffee plants.
Tea and coffee plants require a cool, humid climate with moderate rainfall and well-drained soil. The mountainous regions provide these conditions, with temperatures that are not too high and a consistent supply of moisture from rainfall or mist. The altitude also plays a role, as higher altitudes often have cooler temperatures and more consistent weather patterns, which are beneficial for the slow and steady growth of tea and coffee plants.
Other crops, such as cotton, ragi, and millets, are not as well-suited to mountain soil. Cotton, for example, requires a warm, dry climate and is typically grown in regions with alluvial or black soils. Ragi and millets are more suited to dry, arid regions and do not require the high organic content and well-drained nature of mountain soil. Paddy, on the other hand, requires a warm, humid climate and a lot of water, which is typically found in lowland areas with alluvial soils.
Therefore, the correct answer is tea and coffee, as these crops are the most suitable for the specific conditions provided by mountain soil and the climatic environment of mountainous regions.