Which of the following is not a correct for iso - electronic ions ?

Options

A. They have the same number of electrons around their nuclei
B. Higher the atomic number higher will be positive charge in a series of isoelectronic ions of same period
C. Isoelectronic ions have same electric charge
D. An isoelectronic series may have both positively and negatively charged ions

Answer

To determine which statement is not correct for isoelectronic ions, let's analyze the concept of isoelectronic species and the statements provided.

### Step-by-Step Solution:

1. **Understanding Isoelectronic Ions**:
- Isoelectronic ions are ions that have the same number of electrons. For example, ions like N³⁻, O²⁻, F⁻, and Ne all have 10 electrons.

2. **Evaluating the First Statement**:
- The first statement claims that "they have the same number of electrons around the nuclei."
- This statement is **correct** because by definition, isoelectronic ions have the same number of electrons.

3. **Evaluating the Second Statement**:
- The second statement says, "higher the atomic number, higher will be the positive charge in a series of isoelectronic ions of the same period."
- This statement is also **correct**. As we move across a period, the atomic number increases, which means the number of protons (positive charge) increases while the number of electrons remains the same in isoelectronic ions.

4. **Evaluating the Third Statement**:
- The third statement asserts that "isoelectronic ions have the same electric charge."
- This statement is **not correct**. Isoelectronic ions can have different charges. For example, N³⁻, O²⁻, F⁻, Na⁺, and Mg²⁺ are all isoelectronic with 10 electrons, but they have different charges.

5. **Conclusion**:
- The statement that is not correct for isoelectronic ions is that they have the same electric charge.

### Final Answer:
The statement that is not correct for isoelectronic ions is: "Isoelectronic ions have the same electric charge."

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