All three plants—Groundnut (Arachis hypogea), Horse-gram (Macrotyloma uniflorum), and Soybean (Glycine max)—belong to the Fabaceae family, commonly known as the pea family or legume family. This family is characterized by plants that produce pods with seeds, enriching soil fertility through nitrogen fixation, a vital ecological and agricultural function. Understanding the classification and ecological roles of these plants is crucial for UPSC Prelims, as it highlights the significance of biodiversity and sustainable agricultural practices in environmental science, a key area of the syllabus.