CONCEPT: Bio-mass energy: - Bio-mass is the energy source that is received from animal wastes and plant materials. - For example, cow-dung, various plant materials like the residue after harvesting the crops, vegetable waste, and sewage are decomposed in the absence of oxygen to give biogas. EXPLANATION: - From the above, it is clear that wood, gobar- gas, and cow-dung are an example of a biomass energy source. Therefore option 1,2 , and 4 is not a bio-mass energy source. - On the other hand, nuclear energy is obtained from nuclear fusion and fission. Therefore option 2 is the answer.