$A$ single-electron species has a nuclear charge of $+Ze$,where $Z$ is a constant. The energy required to excite an electron from the $2^{nd}$ Bohr orbit to the $3^{rd}$ Bohr orbit is $47.2 \ eV$. Calculate the value of $Z$.

Which of the graphs shown below does not represent the relationship between incident light and the electron ejected from a metal surface?

The energy of an electron in the $n^{th}$ orbit of a hydrogen atom is given by:

When electromagnetic radiation of wavelength $300 \, nm$ falls on the surface of sodium,electrons are emitted with a kinetic energy of $1.68 \times 10^{5} \, J \, mol^{-1}$. What is the minimum energy needed to remove an electron from sodium? What is the maximum wavelength that will cause a photoelectron to be emitted?

The ratio of the velocity of an electron in the second orbit of $He^{+}$ to the third orbit of $B^{4+}$ is:

In the Bohr model of the atom,when an electron undergoes a transition from $n = 1$ to $n = 3$,the energy absorbed or emitted is ........