If two protons and two neutrons are added to the nucleus of a carbon atom, what nucleus does it become?

If two protons are added to carbon, the chemical identity changes to oxygen, which is two spaces over horizontally on the periodic table. The number of protons is what we call the atomic number (Z), and this is what defines the identity of an element. Since we also added two neutrons, this is simply oxygen, or oxygen-16, the most abundant isotope of oxygen.