Final answer:
The mass number of a nitrogen atom with 7 protons and 7 neutrons is 14. Nitrogen has an atomic number of 7 and, thus, 7 electrons, which fill two electron shells according to its electron configuration of 1s² 2s² 2p³.
Step-by-step explanation:
The mass number of an atom is calculated by adding together the number of protons and neutrons in the atom's nucleus. For a nitrogen atom with 7 protons and 7 neutrons, the correct mass number would be the sum of these two values. The atomic number of nitrogen is 7, indicating that there are 7 protons in the nucleus of the nitrogen atom. The number of electrons typically equals the number of protons in a neutral atom, so there would also be 7 electrons.
When describing the electron distribution, we say that nitrogen has 7 electrons which will fill the first and second electron shells. The electron configuration for nitrogen will start by filling the 1s orbital, followed by the 2s and then the 2p orbitals. The correct electron configuration for nitrogen is 1s² 2s² 2p³, implying it has two electron shells.
This electron configuration reflects how the electrons are distributed across different energy levels, and based on this, one can deduce that nitrogen likely has two electron shells.