The maximum wavelength of radiation that can ionise a sodium atom is $2414 \ \mathring{A}$. The ionisation energy of sodium per mole shall be

$A$ $50 \, W$ bulb emits monochromatic red light of wavelength $795 \, nm$. The number of photons emitted per second by the bulb is $x \times 10^{20}$. The value of $x$ is $......$.
$[ \text{Given} : h=6.63 \times 10^{-34} \, J \cdot s \text{ and } c=3.0 \times 10^{8} \, m \cdot s^{-1} ]$

The figure that is not a direct manifestation of the quantum nature of atoms is:

Four lowest energy levels of $H$-atom are shown in the figure. The number of emission lines could be obtained by transitions from these levels. The total number of possible emission lines is:

How much energy is required to ionize a $H$ atom if the electron occupies the $n=5$ orbit? Compare your answer with the ionization enthalpy of the $H$ atom (energy required to remove the electron from the $n=1$ orbit).

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: