The wave nature of electrons was experimentally verified by,

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

This question has Statement-$1$ and Statement-$2$. Of the four choices given after the Statements,choose the one that best describes the two Statements.
Statement-$1$: Davisson-Germer experiment established the wave nature of electrons.
Statement-$2$: If electrons have wave nature,they can interfere and show diffraction.

$A$ sodium atom is in one of the states labeled 'Lowest excited levels'. It remains in that state for an average time of $10^{-8} \, s$,before it makes a transition back to a ground state. What is the uncertainty in energy of that excited state?

What is a wave packet? Explain using a necessary diagram.

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