Question

Find the number of neutrons and protons in an atom with atomic number 39 and mass number 89?

• A. 39 protons and 39 neutrons
• B. 39 protons and 50 neutrons
• C. 39 protons and 89 neutrons
• D. 50 protons and 39 neutrons
• E. 50 protons and 50 neutrons

Answer 1

Answer: (B)

39 protons and 50 neutrons

Number of protons is equal to the atomic number. It is 39.
Number of neutrons is equal to the difference between mass number and atomic number.
It is $89-39=50$