what sentence describes all atoms of one element A. They have the same number of isotopes B. They have the same properties C. They have the same number of protons D. They have the same number of neutrons

C. They have the same number of protons.

Explanation:

Even though in isotopes, there's uneven number of neutrons, there's always same number of protons.

Hope it helps.

radioactive decay occurs in unstable atomic nuclei – that is, ones that don't have enough binding energy to hold

the nucleus together due to an excess of either protons or neutrons.

it's all four options.