• question_answer Hydrogen atoms are excited from ground state to the principal quantum number 4. Then the number of spectral lines observed will be A)  3                    B)  6C)  5                    D)  2

The number of spectral lines observed from quantum number n is $\frac{n(n-1)}{2}.$ When n = 4, number of lines is $\frac{4(4-1)}{2}=6$ Hence, the correction option is [b].