Question

which subatomic particles are not in the nucleus?
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what do an ion of ca and an atom of ar have in common?
an ion of ca²⁺ and an atom of ar have the same number of electrons, but a different number of protons in their atoms.
an ion of ca²⁺ and an atom of ar have the same total number of protons and neutrons, but a different number of electrons.
there are no similarities between the two.

Explanation:

1. Atoms consist of a nucleus containing protons and neutrons, with electrons orbiting outside the nucleus. So electrons are the sub - atomic particles not in the nucleus.
2. A calcium ion ($Ca^{2+}$) has lost 2 electrons. Calcium (Ca) has an atomic number of 20, so $Ca^{2+}$ has 18 electrons. Argon (Ar) has an atomic number of 18 and also has 18 electrons. So an ion of $Ca^{2+}$ and an atom of Ar have the same number of electrons.

Answer:

1. Electrons
2. An ion of $Ca^{2+}$ and an atom of Ar have the same number of electrons.