Final answer:
The K shell or the innermost shell of an atom produces the least amount of energy, as its electrons are most tightly bound to the nucleus.
Step-by-step explanation:
The shell that produces the least amount of energy is the K shell (A). The shells of an atom can be thought of as levels of energy that electrons occupy, with the K shell being the innermost shell. This shell is closest to the nucleus and its electrons are bound most tightly to the nucleus, which means that these electrons have the lowest energy.
As we move to outer shells such as the L, M, and N shells, the electrons are less tightly bound, and therefore, these shells represent higher energy levels. This is reflected in how the atom's reactivity and chemical behavior are influenced by the electrons in the outermost shells due to their weaker attraction to the nucleus, making them more accessible for chemical reactions.