Amongst the following, the maximum number of isoelectronic molecules/ions are
`XeO_(3), BrO_(3)^(-), ClF, XeF_(2), OF_(2), XeF_(4), ICl_(4)^(-), ClO^(-), IBr_(2)^(-)`.

Explanation

To determine which of the given molecules/ions are isoelectronic, we need to calculate the total number of electrons for each species. Isoelectronic species have the same number of electrons.

Let's go through each molecule/ion step by step:

### Step 1: Calculate the number of electrons for each species.

1. **XeO₃**:
- Xenon (Xe) has 54 electrons.
- Each Oxygen (O) has 8 electrons, and there are 3 Oxygens.
- Total = 54 + (3 × 8) = 54 + 24 = **78 electrons**.

2. **BrO₃⁻**:
- Bromine (Br) has 35 electrons.
- Each Oxygen (O) has 8 electrons, and there are 3 Oxygens.
- The negative charge adds 1 electron.
- Total = 35 + (3 × 8) + 1 = 35 + 24 + 1 = **60 electrons**.

3. **ClF**:
- Chlorine (Cl) has 17 electrons.
- Fluorine (F) has 9 electrons.
- Total = 17 + 9 = **26 electrons**.

4. **XeF₂**:
- Xenon (Xe) has 54 electrons.
- Each Fluorine (F) has 9 electrons, and there are 2 Fluorines.
- Total = 54 + (2 × 9) = 54 + 18 = **72 electrons**.

5. **OF₂**:
- Oxygen (O) has 8 electrons.
- Each Fluorine (F) has 9 electrons, and there are 2 Fluorines.
- Total = 8 + (2 × 9) = 8 + 18 = **26 electrons**.

6. **XeF₄**:
- Xenon (Xe) has 54 electrons.
- Each Fluorine (F) has 9 electrons, and there are 4 Fluorines.
- Total = 54 + (4 × 9) = 54 + 36 = **90 electrons**.

7. **ICl₄⁻**:
- Iodine (I) has 53 electrons.
- Each Chlorine (Cl) has 17 electrons, and there are 4 Chlorines.
- The negative charge adds 1 electron.
- Total = 53 + (4 × 17) + 1 = 53 + 68 + 1 = **122 electrons**.

8. **ClO⁻**:
- Chlorine (Cl) has 17 electrons.
- Oxygen (O) has 8 electrons.
- The negative charge adds 1 electron.
- Total = 17 + 8 + 1 = **26 electrons**.

9. **IBr₂⁻**:
- Iodine (I) has 53 electrons.
- Each Bromine (Br) has 35 electrons, and there are 2 Bromines.
- The negative charge adds 1 electron.
- Total = 53 + (2 × 35) + 1 = 53 + 70 + 1 = **124 electrons**.

### Step 2: Identify the isoelectronic species.

Now we can summarize the total number of electrons for each species:

- **XeO₃**: 78 electrons
- **BrO₃⁻**: 60 electrons
- **ClF**: 26 electrons
- **XeF₂**: 72 electrons
- **OF₂**: 26 electrons
- **XeF₄**: 90 electrons
- **ICl₄⁻**: 122 electrons
- **ClO⁻**: 26 electrons
- **IBr₂⁻**: 124 electrons

From the calculations, we can see that the following species have the same number of electrons:

- **ClF** (26 electrons)
- **OF₂** (26 electrons)
- **ClO⁻** (26 electrons)

Thus, there are **three isoelectronic species**: ClF, OF₂, and ClO⁻.

### Conclusion:
Among the given molecules/ions, the maximum number of isoelectronic species is **3**.

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