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.

the best answer is d because the strong cohesion is caused by the ability of water molecules to undergo hydrogen bonding.

a is incorrect because when water solidifies, it becomes   ice, which expands and occupies a bigger volume for the same mass of water in its liquid state.

b is incorrect because water has high surface tension. besides bonding to itself it hydrogen bonds to other molecules at the top decreasing possibility for breaking of attractive forces.

c is incorrect because the water molecule has oxygen which is highly electronegative and so pulls the electron pair towards itself creating a dipole moment, making the molecule polar.

e is incorrect because water has strong adhesion, ability to stick to other molecules such as glass because of this molecules having stronger hydrogen bonding than water.