How many neutrons are in an atom of Na-23 (atomic number 11)?

Answer and explanation

Correct answer: D. 12

  1. Step 1: Neutrons = mass number − atomic number. Step 2. 23 − 11 = 12. Answer: 12. Why not the others: 23 is what you get if you give the mass number. 11 is what you get if you give the proton number. 34 is what you get if you add the proton and mass numbers.

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