The correct option is 1, 3, and 4 only, which includes alfalfa, chickpea, and clover as nitrogen-fixing plants. These plants form symbiotic relationships with specific nitrogen-fixing bacteria, such as Rhizobium, that reside in their root nodules, converting atmospheric nitrogen into a form usable by the plants. This process enhances soil fertility and reduces the need for synthetic fertilizers, making them crucial for sustainable agriculture. In contrast, amaranth, purslane, and spinach do not possess this nitrogen-fixing capability, reflecting the importance of understanding plant families and their ecological roles within agricultural systems as highlighted in standard UPSC materials like NCERT textbooks.