As we move across a period in the periodic table from left to right, the atomic radius decreases due to an increase in effective nuclear charge. Among the elements B, C, N, O, and F, fluorine (F) has the smallest atomic radius because it is furthest to the right in the second period.
Thus, the correct answer is (E).
Considering Bohr’s atomic model for hydrogen atom :
(A) the energy of H atom in ground state is same as energy of He+ ion in its first excited state.
(B) the energy of H atom in ground state is same as that for Li++ ion in its second excited state.
(C) the energy of H atom in its ground state is same as that of He+ ion for its ground state.
(D) the energy of He+ ion in its first excited state is same as that for Li++ ion in its ground state.