Answer:
3.equal numbers of protons and neutrons.
Step-by-step explanation:
A stable atom with a large nucleus would contain equal number of protons and neutrons. When the number of protons and neutrons in the nucleus are equal, an atom would attain stability.
Unstable atoms have either the number of protons or neutrons greater. In order for such atoms to attain stability, they give off the excess protons or neutrons. When atoms gives off excess protons or neutrons, they are said to be radioactive.