Aserious risk factor associated with the operation of a nuclear power plant is the production of
(1) acid rain
(2) helium gas
(3) greenhouse gases, such as co2
(4) radioisotopes with long half-lives

Option (4) is the correct answer.

Explanation:

In a nuclear power plant, nuclear fission and fusion reactions occur.

During these reaction a large amount of heat is releases along with the release of radioisotopes. These radioisotopes have long half-lives as a result these emit harmful radiations which can either cause burns or blindness to the people around the nuclear power plant etc.

For example, isotope of Uranium-238 have longer half life.

Thus, we can conclude that a serious risk factor associated with the operation of a nuclear power plant is the production of radioisotopes with long half-lives.

it is b that is the answer.