In the Davisson-Germer experiment,for which value of accelerating voltage was the intensity of the electron beam found to be maximum (in $V$)?

$G$ $P$ Thomson experimentally confirmed the existence of matter waves by the phenomenon of:

Given below are two statements: One is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A:$ The beam of electrons shows wave nature and exhibits interference and diffraction.
Reason $R:$ Davisson-Germer experimentally verified the wave nature of electrons.
In the light of the above statements,choose the most appropriate answer from the options given below:

The Davisson and Germer experiment proved:

The wave nature of electrons suggests that they will produce diffraction effects. Davisson and Germer experimentally proved this by diffracting electrons from a crystal. The law of diffraction from a crystal is obtained from the constructive interference of electron waves reflected from the planes of atoms in the crystal. Electrons accelerated by a potential $V$ are diffracted by a crystal. If $d = 1 \ \mathring{A}$ and $i = 30^\circ$,then the value of $V$ should be ........... $V$. $(h = 6.6 \times 10^{-34} \ J \cdot s, m_e = 9.1 \times 10^{-31} \ kg, e = 1.6 \times 10^{-19} \ C)$

The wave property of electrons implies that they will show diffraction effects. Davisson and Germer demonstrated this by diffracting electrons from crystals. The law governing the diffraction from a crystal is obtained by requiring that electron waves reflected from the planes of atoms in a crystal interfere constructively (see figure).