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

An electron of a stationary Hydrogen atom transitions from the fifth energy level to the ground level. The velocity that the atom acquires as a result of photon emission is ( $m=$ mass of the atom,$R=$ Rydberg's constant,$h=$ Planck's constant).

Match the appropriate pairs from List-$I$ and List-$II$:

List-$I$	List-$II$
$1$. Nitrogen molecules	$(A)$ Continuous spectrum
$2$. Incandescent solids	$(B)$ Absorption spectrum
$3$. Fraunhofer lines	$(C)$ Band spectrum
$4$. Electric arc between iron rods	$(D)$ Emission spectrum

$A$ hydrogen atom emits a photon corresponding to an electron transition from $n = 5$ to $n = 1$. The recoil speed of the hydrogen atom is almost......$m/s$ (mass of proton $\approx 1.6 \times 10^{-27} \ kg$).

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

$A$ neutron collides head-on with a stationary hydrogen atom in its ground state.