Competency #5
Answer and Explanation
The correct answer is E.
Recall that the atomic number (found above the symbol for the element on the periodic table) is always equal to the number of protons for that element. Therefore, we can identify each element by its number of protons alone (the number of neutrons or electrons that were provided only as distracters).
- 6 protons, 6 neutrons, 6 electrons. Since this has 6 protons, it must be some form of Carbon.
- 6 protons, 8 neutrons, 6 electrons. Since this has 6 protons, it must be some form of Carbon.
- 7 protons, 6 neutrons, 7 electrons. Since this has 7 protons, it must be some form of Nitrogen.
- 12 protons, 6 neutrons, 12 electrons. Since this has 12 protons, it must be some form of Magnesium.
- Now, we see that both A & B represent 2 different isotopes of carbon, so the correct choice is "E. Both A & B".
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