Question

From the following pairs of ions which one is not an iso-electronic pair?

• A. Na⁺, Mg²⁺
• B. Mn²⁺, Fe³⁺
• C. Fe²⁺, Mn²⁺
• D. O²⁻, F⁻

Hint:

Species are often iso-electronic if they are neighbors in the periodic table and their charges differ in a way that compensates for their atomic number difference.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Iso-electronic species are atoms or ions that have the same number of electrons. To identify them, we look at the atomic number of the neutral atom and adjust for the charge (subtract for positive charge, add for negative charge).
Step 2: Detailed Explanation:
1. Na⁺ (11-1=10) and Mg²⁺ (12-2=10): Both have 10 electrons. (Iso-electronic)
2. Mn²⁺ (25-2=23) and Fe³⁺ (26-3=23): Both have 23 electrons. (Iso-electronic)
3. Fe²⁺ (26-2=24) and Mn²⁺ (25-2=23): These have different numbers of electrons.
4. O²⁻ (8+2=10) and F⁻ (9+1=10): Both have 10 electrons. (Iso-electronic)
Step 3: Final Answer:
The pair Fe²⁺ and Mn²⁺ is not iso-electronic.