Question

As the size of the nucleus increases, more______are needed to maintain the attractive force.

Answer 1

The answer is Neutrons on Edge.

Answer 2

The attractive force that keeps the nucleus together is called nucleus force.
The nucleus becomes increasingly more stable upon the addition of nucleons up to iron-56.
So, as the size of the nucleus increase more iron 56 are needed.
Iron-56 (56Fe) is the most common isotope of iron.