Question

question 5 ar ar argon 39.9 argon has protons neutrons electrons

Explanation:

Step1: Recall atomic number property

The atomic number is equal to the number of protons. The atomic number of Ar is 18, so the number of protons is 18.

Step2: Calculate number of neutrons

The mass - number is approximately 40 (39.9 rounded). Mass - number = number of protons+number of neutrons. So number of neutrons = mass - number - number of protons = 40 - 18=22.

Step3: Recall electron - proton relationship

In a neutral atom, the number of electrons is equal to the number of protons. So the number of electrons is 18.

Answer:

Protons: 18
Neutrons: 22
Electrons: 18