Answer: C
Explanation: Based on the periodic table, O is atomic number 8, which means it has 8 electrons. The first few atomic orbitals are 1s, 2s, and 2p.Each orbital can hold 2 electrons maximum, and there are 2l+1 of each type of orbital (s,p,d,f,g,...), where l=0 corresponds to an s orbital, l=1 means porbital, and so on. So, the configuration for neutral O atom is: 1s22s22p4. When oxygen gains two electrons, it acquires a charge of 2−. Therefore, the twoelectrons, which go into the highest-energy atomic orbitals, give you a new configuration of1s22s22p6for O2−, which is the same electron configuration as Ne. That is known as a noble-gas-like configuration, and in general it is stable if oxygen is like that in a compound (having 8 electrons in its 2s and 2p orbitals combined).