An $X$-ray pulse of wavelength $4.9\;\mathop A\limits^ \circ $ is sent through a section of Wilson cloud chamber containing a super saturated gas, and tracks of photoelectron ejected from the gaseous atoms are observed. Two groups of tracks of lengths $1.40\;cm$ and $2.02\;cm$ are noted. If the range-energy relation for cloud chamber is given by $R = \alpha E$ with $\alpha = 1cm/keV,$ obtain the binding energies of the two levels from which electrons are emitted. Given $h = 6.63 \times {10^{ - 34}}J - s,e = 1.6 \times {10^{