4p, 3d, 3p, 3s, 2p, 2s and 1s orbitals may be occupied during de-excitation.<span />
Though the ratio of any two atom's masses was the same on either scale, it was horribly confusing, so in 1961, a compromise was reached. Instead of using either Hydrogen, or Oxygen as the standard, the isotope of Carbon<span> with 6 </span>protons<span> and 6 neutrons in its nucleus (</span>Carbon-12<span>) was given a mass of exactly 12.</span>
Answer b) a to c would be considered one wavelength.
