The qualitative order of the de-Broglie wavelength for electron, proton and alpha particle is ${\mathrm{\lambda }}_{\mathrm{e}}>{\mathrm{\lambda }}_{\mathrm{p}}>{\mathrm{\lambda }}_{\mathrm{\alpha }}$, if

The configuration $\left[\mathrm{Ar}\right]3{\mathrm{d}}^{10}4{\mathrm{s}}^{2}4{\mathrm{p}}^4$ is similar to that of:

$\left(\mathrm{a}\right)$ Using Bohr's model for hydrogen atom, find the speed of electron in the first orbit if the Bohr's radius is ${\mathrm{a}}_0=0.529\times {10}^{-10} \mathrm{m}.$ Find de Broglie wavelength of the electron also.

$\left(\mathrm{b}\right)$ Find the orbital angular momentum of electron if it is in $2\mathrm{p}$ orbital of $\mathrm{H}$ in terms of $\frac{\mathrm{h}}{2\mathrm{\pi }}.$

The work function $\left({\mathrm{W}}_0\right)$ of some metals is listed below. Count the number of metals which will show photoelectric effect when light of $300 \mathrm{nm}$ wavelength falls on the metal.