The ratio of kinetic energies of photoelectrons emitted from a metal by light of frequencies $v_1$ and $v_2$ is $1 : 2$. The threshold frequency of the metal will be:

If in Bohr's model,for a unielectronic atom,the time period of revolution is represented as $T_{n,Z}$ where $n$ represents the shell number and $Z$ represents the atomic number,then the value of $T_{1,2} : T_{2,1}$ will be

The energy of an $H$ atom in the $n^{th}$ orbit is $E_n$. What will be the energy of the $n^{th}$ orbit of a singly ionized helium atom $(He^+)$?

The work function of a metal $M$ is $6.3 \ eV$. The wavelength of the incident radiation required to just eject the electrons from its surface (in $nm$) is

The ionization energy of a hydrogen atom is $13.6 \, eV$. What is the energy required (in $eV$) to excite the electron from the ground state to the first excited state?

Bohr's atomic model is applicable to which of the following?