Well, with the light spectrum there technically is no middle color. Both green and yellow meet up in the middle at 560 nm (wavelength interval) and 540 THz (frequency interval).
Here are the answers to the question. Make sure to give a valid reason, please.
A. the sum of the protons and neutrons in one atom of the element.
B. a ratio based on the mass of a carbon-12 atom.
C. a weighted average of the masses of an element's isotopes.
D. twice the number of protons in one atom of the element.