Question

Beryllium has an atomic number of 4. How many neutrons does the isotope beryllium-9 have?.

Answer 1

Answer: 5 neutrons

Step-by-step explanation:

atomic number - number of protons in the nucleus

beryllium has mass number 9

mass number = number of protons + number of neutrons

9 = 4 + number of neutrons

number of neutrons = 9-4 = 5