Question

What are radioisotopes? and Are they harmful to humans?

Answer 1

They are isotopes that emit alpha, beta, or gamma rays. Some are harmful. Google radioactivity to read about it.

Answer 2

well, first, isotopes are different masses of atoms of the same element.
In other words they have the same number of protons
but a different number of neutrons.
Now some such isotopes are unstable. Some like carbon 14 (regular carbon 12 with two extra neutrons) take a long time, like many years, to break up. Others break up in seconds or minutes. When they break up they are likely to emit energy and particles, perhaps even protons resulting in new elements. Dangerous particles and rays in the gamma ray to Xray region often result and are harmful.