Hint: It is the other name of red gram. The scientific name is Cajanus cajan. It is a pulse crop belonging to the Febacea family. It is an example of a leguminous crop. The other examples of leguminous crops include peas,beans and some other pulses. We need to concentrate on nutritional composition of pulses.
Complete answer: By now, you will almost be able to answer the question. As I mentioned it is a pulse crop, we shall discuss it. The terms legume and pulse have their own distinct meaning though used interchangeably. Legume is the crop which belongs to the Febacea family and has nodules in its roots that help in fixation of atmospheric nitrogen. The edible seed which is obtained from the legume plant is called a pulse. To be specific,the pod is called a legume and the side within it is a pulse. All the pulses are a great source of proteins which acts as a substitute for meat. As vegetarians do not consume meat, they can include pulses in their diet. As pigeon pea is an example of pulse crop,we can conclude that it is a good source of protein.
Hence the correct answer to this question is proteins.
Note: Leguminous crops have root nodules that can fix nitrogen. As all proteins are made of amino acids in which nitrogen is the main component,there is a direct relation between proteins and nitrogen fixation. For this reason, pulses are said to be an important source for plant based proteins. The pigment called leghaemoglobin is present in root nodules that help in nitrogen fixation.