If an economy is inefficient, its actual output combination will lie the production possibilities curve.

Inside. 

If the economy is inefficient, its actual output combination will lie inside the production possibilities curve. This curve represents the opportunities for production in a given economy with the most efficiency being gained by producing along the curve. Any points within or inside the curve are considered inefficient, whereas points outside the curve are considered unavailable or inaccessible without changes in technology or innovation. 

The  atomic nucleus  is the small, dense region consisting of  protons  and  neutrons  at the center of an  atom, discovered in 1911 by  ernest rutherford based on the 1909  gold foil experiment.