A photon of wavelength 0.1 Ao is emitted by a helium atom as a consequence of the emission of photon. The KE gained by helium atom is
0.05 eV
1.05 eV
2.05 eV
3.05 eV
E=p22m=h22mλ2=6.62×10−3422×4×1.67×10−27×0.1×10−102×11.6×10−19eV=43.82×10−6821.376×10−68=2.05eV