If the radius of the second Bohr orbit of the $He^{+}$ ion is $105.8 \, pm$, what is the radius of the third Bohr orbit of the $Li^{2+}$ ion?

If the wavelength of an electromagnetic radiation is $2000 \ \text{Å}$, what is its energy in ergs?

In the hydrogen spectrum,if an electron transitions from the $6^{th}$ orbit to the $2^{nd}$ orbit through multiple steps,the number of spectral lines produced is ....

Calculate the radius of the first orbit of $He^{+}$. (in $pm$)

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:

For a $H$-atom,what is the wavelength in $nm$ associated with the transition of an electron from an infinite energy level to the first energy level? (Rydberg constant = $1.097 \times 10^{7} \ m^{-1}$)