Question

what element is this?
argon (ar)
chlorine (cl)
potassium (k)
oxygen

Explanation:

Step1: Count the number of electrons

The number of electrons in an atom is equal to the number of protons (atomic number). By counting the dots (electrons) in the diagram, we find there are 18 electrons.

Step2: Match with atomic number

Argon (Ar) has an atomic number of 18. Chlorine (Cl) has an atomic number of 17, Potassium (K) has an atomic number of 19, and Oxygen has an atomic number of 8.

Answer:

Argon (Ar)