Q 12-12-010JEE MainAIEEE 2012Easy
A hydrogen atom is excited to the state with principal quantum number $n = 4$. The maximum number of photons that this single atom can emit as it returns to the ground state is
Answer: (D) $3$
A single atom emits the most photons by stepping down one level at a time: $4 \to 3 \to 2 \to 1$, i.e. $3$ photons.
(A large sample of atoms can show $\dfrac{n(n - 1)}{2} = 6$ different lines, but one atom makes only one downward path.)
Solution by Sreeraj P, M.Sc Physics