Argon (Ar) is a noble gas with an atomic number of 18. The atomic number represents the number of protons in the nucleus of an atom. To find the number of neutrons in an atom, you need to know its mass number, which is the sum of protons and neutrons in the nucleus.
The most common isotope of argon, Argon-40, has a mass number of 40. Since the atomic number of argon is 18, the number of neutrons can be calculated as follows:
Number of Neutrons = Mass Number – Atomic Number
Number of Neutrons = 40 – 18 = 22
Therefore, the most common isotope of argon, Argon-40, has 22 neutrons.