The correct option is C 13
The order of energy levels of shells in an atom is K, L, M, N, etc., and according to the Bohr-Bury scheme: the maximum number of electrons in a particular shell is given by 2n2. Since here M shell is the outermost shell, it means that the inner shells are completely filled, i.e. K shell has 2 electrons and the L shell has 8 electrons. The M shell comes after the L shell and it has only 3 electrons.
Therefore, the total number of electrons in the atom of the element = 2 + 8+ 3
= 13 electrons
Since the atom is neutral,
Atomic number of the element = total number of electrons = 13