Answer: 8 protons and 10 neutrons
Step-by-step explanation:
Atomic number is defined as the number of protons or number of electrons that are present in an atom.
Atomic number = Number of electrons = Number of protons
atomic number = 8 = Number of protons
Mass number is defined as the sum of number of protons and neutrons that are present in an atom.
Mass number = Number of protons + Number of neutrons
Mass number = 18 = Number of protons + Number of neutrons
Thus Number of neutrons =18 - Number of protons= 18 - 8 = 10
Thus there are 8 protons and 10 neutrons in Oxygen -18.