MCQ
Number of spectral lines obtained in $\mathrm{He}^{+}$spectra, when an electron makes transition from fifth excited state to first excited state will be
- A$11$
- ✓$10$
- C$12$
- D$13$
✓
Answer
Correct option: B.
$10$
b
$5^{\text {th }} \text { excited state } \Rightarrow n_1=6$
$5^{\text {th }} \text { excited state } \Rightarrow n_1=6$
$1^{\text {st }} \text { excited state } \Rightarrow n_2=2$
$\Delta n=n_1-n_2=6-2=4$
Maximum number of spectral lines
$=\frac{\Delta \mathrm{n}(\Delta \mathrm{n}+1)}{2}=\frac{4(4+1)}{2}=10$
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