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

Pick out the correct statement from the following:

Consider the following two statements $A$ and $B$ and identify the correct choice in the given answers:
$A :$ Line spectra are due to atoms in the gaseous state.
$B :$ Band spectra are due to molecules.

An electron collides with an atom in its ground state. The atom then emits a photon of energy $E_{photon}$. In this process,the change $\Delta E_{elec}$ in the electron's energy is

When the potential of the second excited state of an atom is $108.8 \ V$,the recoil energy of the atom is ...... Joules.

The nature of the sun's spectrum is