Explanation:

Alfalfa, also called lucerne, is a perennial flowering plant in the legume family Fabaceae. It is cultivated as an important forage crop in many countries around the world. Symbiotic N2 fixation by alfalfa provides substantial amounts of nitrogen (N) to livestock operations, subsequent crops, and soil organic matter. Hence option 1 is correct.

Amarnath: Amaranthus is a cosmopolitan genus of annual or short-lived perennial plants collectively known as amaranths. Hence option 2 is not correct.

Chickpea: The chickpea or chick pea is an annual legume of the family Fabaceae. Hence option 3 is correct.

Clover: Nitrogen is "fixed" in clovers through a symbiotic relationship with Rhizobium bacteria that infects the plant's roots. Hence option 4 is correct.

Purslane: Purslane is a green, leafy vegetable that can be eaten raw or cooked. It is known scientifically as Portulaca oleracea, and is also called pigweed, little hogweed, fatweed and pusley. This succulent plant contains about 93% water. It has red stems and small, green leaves. Hence option 5 is not correct.

Spinach: Spinach is a leafy green flowering plant native to central and western Asia. It is of the order Caryophyllales, family Amaranthaceae. Hence option 6 is not correct