Which one of the following corresponds to the wavelength of a line in the Balmer series of the $H$ atom spectrum? $(R =$ Rydberg constant$)$

The wavelength corresponding to an electronic transition between two orbits of a hydrogen atom is $912 \mathring{A}$. The wavelength (in $\mathring{A}$) for the same electronic transition in $Li^{2+}$ is

The ionization enthalpy of a hydrogen atom is $1.312 \times 10^6 \, J \, mol^{-1}$. The energy required to excite an electron from $n = 1$ to $n = 2$ in the atom is .......

The energy of an electron in the excited hydrogen atom is $-3.4 \ eV$. Then according to Bohr's theory,the angular momentum of the electron in that excited state is ($h=$ Planck's constant).

The work function for a metal is $4 \, eV$. To emit a photo electron of zero velocity from the surface of the metal,the wavelength of incident light should be : ................ $\mathring{A}$

Threshold frequency,$v_0$ is the minimum frequency which a photon must possess to eject an electron from a metal. It is different for different metals. When a photon of frequency $1.0 \times 10^{15} \ s^{-1}$ was allowed to hit a metal surface,an electron having $1.988 \times 10^{-19} \ J$ of kinetic energy was emitted. Calculate the threshold frequency of this metal. Show that an electron will not be emitted if a photon with a wavelength equal to $600 \ nm$ hits the metal surface.