To solve the question "Which of the following is not correct for isoelectronic ions?", we need to understand the concept of isoelectronic ions and analyze the provided options step by step.
### Step-by-Step Solution:
1. **Define Isoelectronic Ions**:
Isoelectronic ions are ions that have the same number of total electrons. For example, the ions N³⁻, O²⁻, and F⁻ all have 10 electrons.
2. **Analyze the Options**:
We need to evaluate each option to determine which statement is incorrect regarding isoelectronic ions.
3. **Option 1**: "Isoelectronic ions have the same number of electrons."
- This statement is true because, by definition, isoelectronic ions must have the same number of electrons.
4. **Option 2**: "Higher the atomic number, higher will be the positive charge in a series of isoelectronic species of the same period."
- This statement is also true. As you move across a period in the periodic table, the atomic number increases, which means the number of protons (and thus the positive charge) also increases.
5. **Option 3**: "Isoelectronic ions have the same electric charge."
- This statement is false. Isoelectronic ions can have different charges. For example, N³⁻, O²⁻, F⁻, Ne, Na⁺, and Mg²⁺ are all isoelectronic with 10 electrons, but they have different charges (3-, 2-, 1-, 0, +1, +2 respectively).
6. **Option 4**: "The isoelectronic series may have both positively and negatively charged ions."
- This statement is true. Isoelectronic series can include both anions (negatively charged) and cations (positively charged), as seen in the previous example.
7. **Conclusion**:
Based on the analysis, the statement that is not correct for isoelectronic ions is **Option 3**: "Isoelectronic ions have the same electric charge."
### Final Answer:
**Option 3** is not correct for isoelectronic ions.
