The photoelectric effect can be caused by which of the following?

Which emission transition series is obtained when an electron jumps from $n_2 = \infty$ to $n_1 = 1$?

Wavelengths of different radiations are given below:
$\lambda(A) = 300 \ nm$
$\lambda(B) = 300 \ \mu m$
$\lambda(C) = 3 \ nm$
$\lambda(D) = 30 \ \mathring{A}$
Arrange these radiations in the increasing order of their energies.

$A$ photon of $300 \, nm$ is absorbed by a gas and then re-emits two photons. One re-emitted photon has a wavelength of $496 \, nm$. The wavelength of the second re-emitted photon is: (in $, nm$)

In the hydrogen spectrum,the various lines of the Lyman series lie in the $.......$ region.

Electromagnetic radiation of wavelength $663 \ nm$ is just sufficient to ionise the atom of metal $A.$ The ionization energy of metal $A$ in $kJ \ mol^{-1}$ is ...... .
(Rounded-off to the nearest integer) $\left[ h = 6.63 \times 10^{-34} \ Js, c = 3.00 \times 10^{8} \ ms^{-1}, N_{A} = 6.02 \times 10^{23} \ mol^{-1} \right]$