Out of the listed plants, the following are nitrogen-fixing plants:

1. Alfalfa
2. Chickpea
3. Clover These plants have a symbiotic relationship with bacteria called rhizobia. The bacteria colonize nodules in the plant's roots and fix atmospheric nitrogen into a usable form (nitrates) that the plant can absorb.

The other options are not nitrogen-fixing plants: 2. Amaranth 5. Purslane (Kulfa) 6. Spinach These plants require nitrogen from the soil but cannot fix it themselves. They rely on soil nitrogen content or applied fertilizers. Remember: Purslane is a weed. If you would have known this piece of information, the question could have been easily solved by simple elimination.

Therefore, the correct answer is (1, 3, 4).