Argon (Ar) has an atomic number of 18 and an atomic mass of 40. How many neutrons are there in an atom of Argon? A. 18 B. 20 C. 22 D. 40
The Correct Answer and Explanation is:
The number of neutrons in an atom can be found by subtracting the atomic number from the atomic mass.
- Atomic number (Z): This represents the number of protons in the atom, which for Argon (Ar) is 18.
- Atomic mass (A): This is the total number of protons and neutrons in the nucleus, which is given as 40 for Argon.
To find the number of neutrons (N), we use the following formula:N=A−ZN = A – ZN=A−Z
Substituting the values for Argon:N=40−18=22N = 40 – 18 = 22N=40−18=22
So, Argon has 22 neutrons.
Explanation:
- The atomic number of Argon (18) tells us that it has 18 protons in its nucleus. This number of protons defines the element and its chemical behavior.
- The atomic mass of Argon (approximately 40) refers to the total mass of the nucleus, which is the sum of protons and neutrons.
- Since the number of protons is 18, we subtract that from the atomic mass (40) to find the number of neutrons.
- Thus, the number of neutrons in an Argon atom is 22.
Therefore, the correct answer is C. 22.
