beryllium has four protons in its nucleus. How many neutrons are in beryllium-9? Explain how you calculated your answer

The answer to your question is: 5 neutrons

Explanation:

Beryllium has 4 protons

# of neutrons in beryllium-9

Atomic number (Z) = 4 (number of protons)

Mass number (A) = 9 (number of protons + neutrons)

Mass number = number of protons + number of neutrons

9 = 4 + number of neutrons

neutrons = 9 - 4

neutrons = 5