Which phrase describes a risk associated with producing energy in a nuclear power plant? a. depletion of atmospheric hydrogen (h2) b. depletion of atmospheric carbon dioxide (co2) c. production of wastes needing long-term storage d. production of wastes that cool surrounding water supplies?

Correct Answer is Option C i.e. production of wastes needing long-term storage.

Reason: 
Most of the nuclear power plant uses nuclear fission reaction for generation of electricity. In a nuclear fission reaction, a radio-active nuclei (high atomic mass) is bombarded with fast moving projectile. This results in nuclear disintegration. The mass defect between product and reactant results in generation of energy. The daughter element generated during this event, may also be radio-active in nature. These materials have extremely high half-life. Hence, this waste product needs to be stored safely for long-time so as to minimize the risk of nuclear contamination. 

Rn in the right answer