There are four atoms A, B, C and D with atomic numbers 9, 11, 13 and 15, respectively. The atom containing less than 8 electrons in the second or L-shell is

Consider an element with atomic number 9 is fluorine (F).

The ground state electronic configuration fluorine is

 $\frac{1{\text{s}}^2}{\text{K}}\frac{2{\text{s}}^{2}2{\text{p}}^5}{\text{L}}$

Therefore, the Bohr’s second shell (L) contains 7 electrons $(<8)$ in fluorine.