What do you understand by isoelectronic species? Name a species that will be isoelectronic with each of the following atoms or ions:
`Ar`

Explanation

### Step-by-Step Solution:

1. **Definition of Isoelectronic Species**:
- Isoelectronic species are atoms, ions, or molecules that have the same number of electrons. This means they exhibit similar electronic configurations, even though they may differ in their atomic numbers or overall charge.

2. **Determine the Number of Electrons in Argon (Ar)**:
- Argon (Ar) has an atomic number of 18. This means that a neutral argon atom has 18 electrons.

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