The disposal of wastes produced in a nuclear power plant poses a big problem because it is:

1. too heavy
2. highly inflammable
3. extremely foul smelling
4. highly radioactive

 (d) highly radioactive

Explanation

The disposal of waste materials produced by the fission of uranium-235 in a nuclear power plant poses a big problem because it is highly radioactive due to which emit harmful radiations. Thus, may cause danger to all living things.