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.

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

From which source are a continuous emission spectrum and a line absorption spectrum simultaneously obtained?

$A$ photon collides with a stationary hydrogen atom in the ground state inelastically. The energy of the colliding photon is $10.2 \ eV$. After a time interval of the order of a microsecond,another photon collides with the same hydrogen atom inelastically with an energy of $15 \ eV$. What will be observed by the detector?

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

The ionisation energy of an electron in the ground state of a helium atom is $24.6 eV$. The energy required to remove both electrons is: (in $eV$)