Which experimental observation correctly account for the phenomenon ?

Options

A. `{:("Experimental observation",,"Phenomenon"),("X-rays spectra",,"Charge on nucleus"):}`
B. `{:("Experimental observation",,"Phenomenon"),(alpha-"particle scattering",,"Quantized electron orbit"):}`
C. `{:("Experimental observation",,"Phenomenon"),("Photoelectric effect",,"The nuclear atom"):}`
D. `{:("Experimental observation",,"Phenomenon"),("Emission spectra",,"Quantization of energy"):}`

Answer

D

Explanation

Emission spectrum is key note of quantisation of energy.