The radioisotope that has the longest half-life is the best to use in powering planet and space exploration vehicles because they can travel farther. which radioisotope is the best to use?

Uranium-238 is the radioisotope which is best to use.

Explanation:

Half-life : The time in which the concentration of a reactant is reduced to half of its original value is called half life period.

As it has been given that radioisotope that has the longest half-life is best to use as power source planet and space exploration vehicles:

Uranium 238 is with the highest value of half life which is equal to years.

14 days is the half-life of phosphorus-32