Propose a reason why a nucleus with 6 protons and no neutrons is unstable.

The stability of an atomic nucleus is determined by the balance between the forces within it. There are two main forces at play: the strong nuclear force, which binds protons and neutrons together, and the electromagnetic force, which causes protons to repel each other because they have the same positive charge.

1. In a nucleus with 6 protons and no neutrons, there are no neutrons to contribute to the strong nuclear force. This force is very strong, but it only acts over very short distances. Neutrons help to "dilute" the repulsive electromagnetic force of the protons, because they contribute to the strong nuclear force but do not add to the electromagnetic force.

2. Without any neutrons, the 6 protons are left to repel each other due to the electromagnetic force. This force acts over much larger distances than the strong nuclear force, and without the neutrons to help counteract it, the repulsion between the protons makes the nucleus unstable.

3. Therefore, a nucleus with 6 protons and no neutrons is unstable because there are not enough particles contributing to the strong nuclear force to counteract the repulsive electromagnetic force between the protons.