The group having isoelectronic species is

Options

A. `O^(-),F^(-), Na^(+), Mg^(2+)`
B. `O^(2-), F^(-), Na^(+), Mg^(2+)`
C. `O^(-), F^(-), Na, Mg^(+)`
D. `O^(2-), F^(-), Na, Mg^(2+)`

Explanation

To determine which group contains isoelectronic species, we need to identify the number of electrons in each species listed in the options. Isoelectronic species are those that have the same number of electrons.

### Step-by-Step Solution:

1. **Identify the species in each option**:
Let's analyze the groups one by one.

2. **Option 1: O⁻, F⁻, Na⁺, Mg²⁺**
- O⁻: Oxygen has an atomic number of 8, so it has 8 electrons. With a -1 charge, it gains 1 electron:
\[ 8 + 1 = 9 \text{ electrons} \]
- F⁻: Fluorine has an atomic number of 9, so it has 9 electrons. With a -1 charge, it gains 1 electron:
\[ 9 + 1 = 10 \text{ electrons} \]
- Na⁺: Sodium has an atomic number of 11, so it has 11 electrons. With a +1 charge, it loses 1 electron:
\[ 11 - 1 = 10 \text{ electrons} \]
- Mg²⁺: Magnesium has an atomic number of 12, so it has 12 electrons. With a +2 charge, it loses 2 electrons:
\[ 12 - 2 = 10 \text{ electrons} \]
- **Conclusion for Option 1**: O⁻ has 9 electrons, while F⁻, Na⁺, and Mg²⁺ all have 10 electrons. Therefore, this group does not contain isoelectronic species.

3. **Option 2: O²⁻, F⁻, Na⁺, Mg²⁺**
- O²⁻: Oxygen has 8 electrons. With a -2 charge, it gains 2 electrons:
\[ 8 + 2 = 10 \text{ electrons} \]
- F⁻: As calculated earlier, F⁻ has 10 electrons.
- Na⁺: As calculated earlier, Na⁺ has 10 electrons.
- Mg²⁺: As calculated earlier, Mg²⁺ has 10 electrons.
- **Conclusion for Option 2**: All species (O²⁻, F⁻, Na⁺, Mg²⁺) have 10 electrons. Therefore, this group contains isoelectronic species.

4. **Option 3: O⁻, F⁻, Na⁺**
- O⁻: As calculated earlier, O⁻ has 9 electrons.
- F⁻: As calculated earlier, F⁻ has 10 electrons.
- Na⁺: As calculated earlier, Na⁺ has 10 electrons.
- **Conclusion for Option 3**: O⁻ has 9 electrons, while F⁻ and Na⁺ have 10 electrons. Therefore, this group does not contain isoelectronic species.

5. **Option 4: O²⁻, F⁻, Na, Mg²⁺**
- O²⁻: As calculated earlier, O²⁻ has 10 electrons.
- F⁻: As calculated earlier, F⁻ has 10 electrons.
- Na: Sodium has 11 electrons (atomic number 11).
- Mg²⁺: As calculated earlier, Mg²⁺ has 10 electrons.
- **Conclusion for Option 4**: O²⁻, F⁻, and Mg²⁺ have 10 electrons, but Na has 11 electrons. Therefore, this group does not contain isoelectronic species.

### Final Answer:
The correct option that contains isoelectronic species is **Option 2: O²⁻, F⁻, Na⁺, Mg²⁺**.