$1$ mole of photons, each of frequency $2500 \ s^{-1}$, would have approximately a total energy of:

The energy of an electron in the first Bohr orbit of the $H$ atom is $-13.6 \ eV$. The magnitude of the energy value of an electron in the first excited state of $Be^{3+}$ is $.......... \ eV$ $(nearest \ integer \ value)$.

What is the maximum number of emission lines when the excited electron of an $H$ atom in $n=6$ drops to the ground state?

In which transition of the hydrogen atom will the emitted radiation have the lowest frequency?

$A$ $25 \ W$ bulb emits monochromatic yellow light of wavelength $0.57 \ \mu m$. Calculate the rate of emission of quanta per second.

The electron energy in a hydrogen atom is given by $E_n = (-2.18 \times 10^{-18})/n^2 \ J$. Calculate the energy required to remove an electron completely from the $n = 2$ orbit. What is the longest wavelength of light in $cm$ that can be used to cause this transition?