$A$ gas absorbs a photon of $355 \ nm$ and emits at two wavelengths. If one of the emissions is at $680 \ nm,$ the other is at : ................. $nm$

The Vijayawada $FM$ radio station broadcasts at a frequency of $103.4 \ MHz$. The wavelength of the corresponding radio waves (in $m$) is

The momentum (in $kg \cdot m/s$) of a photon having $6 \, MeV$ energy is:

Choose the correct statements in reference to the photoelectric effect. $(i)$ There is no time lag between the striking of light and ejection of electrons from the metal surface. $(ii)$ The number of electrons ejected is independent of the intensity of light. $(iii)$ The elements $K$,$Rb$ and $Cs$ can show photoelectric effect when exposed to the beam of light.

The number of the following statements which is/are incorrect is:
$A$. Line emission spectra are used to study the electronic structure.
$B$. The emission spectra of atoms in the gas phase show a continuous spread of wavelength from red to violet.
$C$. An absorption spectrum is like the photographic negative of an emission spectrum.
$D$. The element helium was discovered in the sun by spectroscopic method.

Explain the visible spectrum and the continuous spectrum.