An atom of lead (Pb) has a mass number of 207. How many neutrons are in the nucleus?

A. 130

B. 125

C. 82

D. 84

Answer Explanation:

We find the number of neutrons as follows

Number of neutrons

            = mass number – atomic number

            = 207 – 82

            = 125 neutrons

Therefore, the Correct Answer is B.