Question

How does the nucleus of an atom remains relatively stable?

Answer 1

The strong nuclear force binds nucleons (protons and neutrons) together. It is a very short-range force, which is why it only acts over distances on the scale of atomic nuclei. There is repulsion between the protons, which is why, as the number of protons goes up, more and more neutrons are required to stabilize the nucleus (look at how atomic mass goes up relative to atomic number on a periodic table). More nucleons (protons and neutrons) means more strong force, and more neutrons mean more space between the protons, reducing the repulsion. Together, these effects can produce a stable nucleus.