In the Davisson-Germer experiment,when electrons strike a $Ni$ crystal,which of the following waves are diffracted?

Which of the following statements is incorrect regarding the Davisson-Germer experiment?

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 ....... $V$.
$(h = 6.6 \times 10^{-34}\; J-s, m = 9.1 \times 10^{-31}\; kg, e = 1.6 \times 10^{-19}\; C)$

In the Davisson-Germer experiment,an electron beam of energy $75 \ eV$ falls normally on the surface of a crystal. If the maximum intensity is obtained at an angle of $45^o$ to the direction of the incident beam,then the inter-atomic distance in the lattice plane of the crystal will be .............. $\mathring{A}$

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

Explain the arrangement of the Davisson and Germer experiment.