Which of the following are isoelectronic species, i.e., those having the same number of electrons:
`Na^(o+), K^(o+), Mg^(2+), Ca^(2+), S^(2-), Ar`

Explanation

To determine which of the given species are isoelectronic, we need to find out how many electrons each species has. Isoelectronic species are those that have the same number of electrons.

### Step-by-Step Solution:

1. **Determine the number of electrons in each species:**
- **Na⁺ (Sodium ion)**:
- Neutral sodium (Na) has 11 electrons.
- Since Na⁺ has a +1 charge, it has 11 - 1 = **10 electrons**.
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