What radioactive is?

Answer 1

some atoms have a center that isn't stable. This center sometime looses parts, like a proton or a neutron. That part is released with an enormous amount of power. We call that a radio active rays.

A not stable atom is a radio active element.

That together is radio activity.

Answer 2

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.

Answer 3

For a substance to be radioactive, it has to emit radiation. Radiation is defined as energy emissions, often as electromagnetic waves or subatomic particles.

Answer 4

Radio-Activity is the process when an unstable atomic nucleus naturally looses energy by sending ionizing particles and radiation.