Rutherford's $\alpha$-particle scattering experiment concluded that:

If the radius of the electron orbit in the excited state of a hydrogen atom is $476.1 \ pm$, the energy of the electron in that excited state in $J$ is (Radius and energy of the electron in the first orbit of a hydrogen atom are $52.9 \ pm$ and $-2.18 \times 10^{-18} \ J$ respectively).

The energy of an electron in the $3^{rd}$ orbit of $H$-atom (in $J$) is approximately:

Which of the following statements is incorrect?

The photoelectric behaviour of $K$,$Li$,$Mg$,and $Ag$ metals is shown in the plot below. If light of wavelength $400 \ nm$ is incident on each of these metals,which of them will emit photoelectrons?
[Planck's constant $h=6.626 \times 10^{-34} \ J \ s$; velocity of light $c=3 \times 10^8 \ m \ s^{-1}$; $1 \ eV = 1.6 \times 10^{-19} \ J$]

One energy difference between the states $n = 2$ and $n = 3$ is $E \ eV$,in a hydrogen atom. The ionization potential of the $H$ atom is ............. $E$.