How many protons are in an isotope of sodium with a mass number of 25?
A)25
B)15
C)11
D)14
E)32

Question

Quizplus · Accepted Answer

The atomic number of sodium is 11, which tells us the number of protons in a neutral atom of sodium. The mass number of the isotope is 25, which is the total number of protons and neutrons in the nucleus. To find the number of protons in this isotope, we simply subtract the number of neutrons (which is not given) from the mass number. However, since sodium is a stable element, we know that the number of protons and neutrons must be roughly equal. Therefore, we can estimate that there are 11 protons in this isotope, and the most accurate answer choice is C.

How Many Protons Are in an Isotope of Sodium with a Mass