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

When an electron drops from a higher energy level to a lower energy level,then

Which electron transition in a hydrogen atom requires the largest amount of energy?

How many photons are required to provide $1 \, J$ of energy with a wavelength of $5000 \, \mathring{A}$?

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

If the energy of a photon is $14 \, eV$ and it interacts with a hydrogen atom,which of the following is correct?