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Q.
If an electron in hydrogen atom jumps from an orbit of level $n \,= \,3$ to an orbit of level $n\, =\, 2$, the emitted radiation has a frequency ($R$ = Rydberg constant, $C$ = velocity of light)
Given, $ n_{1}=2 ; \,\,\,\,\, n_{2}=3$
Now, we know that, frequency of an emitted electron,
$v =R c\left(\frac{1}{n_{1}^{2}}-\frac{1}{n_{2}^{2}}\right) $
$=Rc\left(\frac{1}{2^{2}}-\frac{1}{3^{2}}\right)=R c\left(\frac{1}{4}-\frac{1}{9}\right)$
$=\frac{5 R C}{36}$