Question

One isotope of sodium has 11 protons and 7 neutrons. What is the mass number of this isotope?

4
7
11
18

Answer 1

The mass number of an isotope is equal to the sum of protons and neutrons in its nucleus. In this case, the isotope of sodium has 11 protons and 7 neutrons, so the mass number is 11 + 7 = 18. Therefore, the correct answer is 18.