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

Which of the following atoms has the lowest ionization potential?

$A$ 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 $\approx 1.6 \times 10^{-27} \ kg$).

Highly excited states for hydrogen-like atoms (also called Rydberg states) with nuclear charge $Ze$ are defined by their principal quantum number $n$,where $n \gg 1$. Which of the following statement$(s)$ is(are) true?
$(A)$ Relative change in the radii of two consecutive orbitals does not depend on $Z$
$(B)$ Relative change in the radii of two consecutive orbitals varies as $1/n$
$(C)$ Relative change in the energy of two consecutive orbitals varies as $1/n^3$
$(D)$ Relative change in the angular momenta of two consecutive orbitals varies as $1/n$

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 will be:

When the potential energy of the second excited state of an atom is $108.8 \ eV$,the recoil momentum of the atom is ...... $kg \ m/s$.