Question

Hydrogen atoms are excited from ground state to the state of principal quantum number $4$. Then, the number of spectral lines observed will be

• A. $3$
• B. $6$
• C. $5$
• D. $2$

Answer 1

Answer: (B)

$6$

Number of spectral lines $N_E=\frac{n(n-1)}{2}=\frac{4(4-1)}{2}=6$
The following spectral lines could be formed:
$4$ to $1,4$ to $2,4$ to $3$
$3$ to $1,3$ to $2$
$2$ to $1$.
Hence $6$ spectral lines.