If an electron is moving in the $n^{th}$ orbit around the nucleus with a velocity $v$ and radius $r$,then the value of $n$ is .........

The third line in the Balmer series corresponds to an electronic transition between which Bohr's orbits in hydrogen?

For a lithium atom,what can be said about the angular momentum and energy values for the permitted orbit of its third electron?

Which of the following statements are correct,if the threshold frequency of caesium is $5.16 \times 10^{14} \ Hz$?
$A.$ When $Cs$ is placed inside a vacuum chamber with an ammeter connected to it and yellow light is focused on $Cs$,the ammeter shows the presence of current.
$B.$ When the brightness of the yellow light is dimmed,the value of the current in the ammeter is reduced.
$C.$ When a red light is used instead of the yellow light,the current produced is higher with respect to the yellow light.
$D.$ When a blue light is used,the ammeter shows the formation of current.
$E.$ When a white light is used,the ammeter shows the formation of current.
Choose the correct answer from the options given below:

Calculate the wavenumber of a photon emitted during the transition from the orbit of $n=3$ to $n=2$ in a hydrogen atom. $(R_{H} = 109677 \ cm^{-1})$ (in $cm^{-1}$)

The wavenumber of the first line $(n_2=3)$ in the Balmer series of hydrogen is $\bar{\nu}_1 \ cm^{-1}$. What is the wavenumber (in $cm^{-1}$) of the second line $(n_2=4)$ in the Balmer series of $He^{+}$?