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It is just based on the fact that they are closer or further away from the Sun.
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Answer:
<u><em>(B.) a significantly lower mass that protons</em></u>
Explanation:
The mass (in g) of an electron is 9.11 ×g, which is significantly lower than the mass of protons and neutrons which are approximately the same. They are extremely small (equal to 0 amu), contributing nothing to the overall mass of the atom.
The nucleus has a mass of 1 amu and is positively charged.
Their is 2 valence electrons