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

4
7
11
18

1 answer

The mass number of an isotope is calculated by adding the number of protons and neutrons together.

In this case, the isotope of sodium has:

  • 11 protons
  • 7 neutrons

So, the mass number is calculated as follows:

Mass number = Number of protons + Number of neutrons
Mass number = 11 + 7 = 18

Therefore, the mass number of this isotope is 18.