The splitting of a spectral line into groups under the effect of an electric or magnetic field is called:

$Assertion :$ $A$ tube light emits white light.
$Reason :$ Emission of light in a tube takes place at a very high temperature.

An energy of $24.6\ eV$ is required to remove one of the electrons from a neutral helium atom. The energy (in $eV$) required to remove both the electrons from a neutral helium atom is

If in nature there may not be an element for which the principal quantum number $n > 4,$ then the total possible number of elements will be

An electron of a stationary hydrogen atom passes from the fifth energy level to the ground level. The velocity that the atom acquired as a result of photon emission will be

The colour of the positive column in a gas discharge tube depends on