Can someone explain what radioisotopes are?

A radioisotope is a radioactive isotope.

Explanation:

On the Periodic Table, elements 92 and up are radioactive. So that is Uranium and any higher elements. Remember that radioactive elements love to decay and are dangerous.

Isotopes are different forms of an element. For instance, we could have different amount of neutrons in the same element (same number of protons).

We could have an element like He - 4 vs. He - 6, where He - 4 would have 2 neutrons and He - 6 would have 4 neutrons.

So a radioisotope would be an elemental isotope that is radioactive. A good example of this is Uranium.

We have thousands of different isotopes of Uranium, but 2 are well known: Uranium - 235 and Uranium - 238. Both are the same element with the same amount of protons, but both have a different amount of neutrons.

indium, and thallium have three electrons i think