Cowpea is the non-oil crop among the following.
While coconut, beniseed (sesame), and melon are all oil crops that are grown primarily for their oil-rich seeds, cowpea is a legume crop that is grown for its edible seeds, which are rich in protein and other nutrients. Cowpea is commonly consumed as a food crop in many parts of the world, and it is also used as a forage crop for livestock.
Unlike coconut, beniseed, and melon, which are all highly valued for their oil content, cowpea is not typically grown for oil production. While it does contain some oil, the oil content of cowpea seeds is relatively low compared to oil crops like coconut and beniseed. Instead, cowpea is grown primarily for its nutritional value and as a source of protein for human and animal consumption.
So, of the options given, cowpea is the non-oil crop, as it is not primarily grown for its oil content.