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

Consider two separate ideal gases of electrons and protons having the same number of particles. The temperature of both gases is the same. The ratio of the uncertainty in determining the position of an electron to that of a proton is proportional to :-

Match List $-I$ (Experiment performed) with List $-II$ (Phenomena discovered/associated) and select the correct option from the options given below:

List $-I$	List $-II$
$(1)$ Davisson and Germer	$(i)$ Wave nature of electrons
$(2)$ Millikan's oil drop experiment	$(ii)$ Charge of an electron
$(3)$ Rutherford experiment	$(iii)$ Quantisation of energy levels
$(4)$ Franck-Hertz experiment	$(iv)$ Existence of nucleus

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).
Electrons accelerated by potential $V$ are diffracted from a crystal. If $d = 1\; \text{\AA}$, and $i = 30^{\circ}$, $V$ should be about ....... $V$.
$(h = 6.6 \times 10^{-34}\; J-s, m = 9.1 \times 10^{-31}\; kg, e = 1.6 \times 10^{-19}\; C)$

Given below are two statements :-
Statement $I$ : Davisson-Germer experiment establishes the wave nature of electrons.
Statement $II$ : If electrons have wave nature,they can interfere and show diffraction.
In the light of the above statements,choose the correct answer from the options given below:

In the Davisson and Germer experiment,the velocity of electrons emitted from the electron gun can be increased by