Number of species that are isoelectronics with `Sr^(2+)` ion are four.

Explanation

To determine the number of species that are isoelectronic with the `Sr^(2+)` ion, we will follow these steps:

### Step 1: Understand Isoelectronic Species
Isoelectronic species are atoms or ions that have the same number of electrons. Therefore, to find species that are isoelectronic with `Sr^(2+)`, we first need to determine how many electrons this ion has.

### Step 2: Determine the Electron Count of `Sr^(2+)`
Strontium (Sr) has an atomic number of 38, which means it has 38 electrons in its neutral state. Since `Sr^(2+)` has a +2 charge, it has lost 2 electrons.

**Calculation:**
- Number of electrons in neutral Sr = 38
- Number of electrons in `Sr^(2+)` = 38 - 2 = 36 electrons

### Step 3: Identify Species with 36 Electrons
Now, we need to find other species that also have 36 electrons.

1. **Bromide Ion (Br⁻)**:
- Bromine (Br) has an atomic number of 35, which means it has 35 electrons in its neutral state. The bromide ion (Br⁻) gains one electron.
- Total electrons in Br⁻ = 35 + 1 = 36 electrons.

2. **Krypton (Kr)**:
- Krypton (Kr) is a noble gas with an atomic number of 36, which means it has 36 electrons in its neutral state.

3. **Rubidium Ion (Rb⁺)**:
- Rubidium (Rb) has an atomic number of 37, which means it has 37 electrons in its neutral state. The rubidium ion (Rb⁺) loses one electron.
- Total electrons in Rb⁺ = 37 - 1 = 36 electrons.

### Step 4: Count the Isoelectronic Species
From our findings, we have identified the following species that are isoelectronic with `Sr^(2+)`:
- `Br⁻`
- `Kr`
- `Rb⁺`

Thus, we have found **three species** that are isoelectronic with `Sr^(2+)`, not four as stated in the question.

### Conclusion
The statement that the number of species that are isoelectronic with `Sr^(2+)` is four is **false**.

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