Neutral atoms of argon, atomic number 18, have the same number of electrons as each of the following items except: Cl - S - 2 K + Ca + 2 Ne

Ne.

Explanation:

Neutral argon, atomic number 18, has 18 electrons.

Cl⁻:

Neutral atom of Cl, atomic number 17, has 17 electrons.

When it gains electron and be Cl⁻, then it has 18 electrons a neutral Ar.

S²⁻:

Neutral atom of S, atomic number 16, has 16 electrons.

When it gains 2 electrons and be S²⁻, then it has 18 electrons a neutral Ar.

K⁺:

Neutral atom of K, atomic number 19, has 19 electrons.

When it losses electron and be K⁺, then it has 18 electrons a neutral Ar.

Ca²⁺:

Neutral atom of Ca, atomic number 20, has 20 electrons.

When it losses 2 electrons and be Ca²⁺, then it has 18 electrons a neutral Ar.

Ne:

It is a noble gas that has 10 electrons.

So, the right choice is: Ne.