In which two metals in the following pairs the difference between the ionic radii is maximum?

Options

A. `K, Ca`
B. `Mn , Fe`
C. `Co, Ni`
D. `Cr, Mn`

Answer

To determine which two metals in the given pairs have the maximum difference in ionic radii, we will analyze the ionic radii of the metals in the context of their positions in the periodic table and their respective charges.

### Step-by-Step Solution:

1. **Identify the Metals and Their Ionic Forms**:
- We need to consider the pairs of metals provided in the question. For this example, let's assume the pairs are Potassium (K) and Calcium (Ca), as well as some transition metals like Manganese (Mn) and Iron (Fe).

2. **Understand Ionic Radii**:
- Ionic radii refer to the size of an ion in a crystal lattice. The size of cations (positively charged ions) generally decreases with an increase in positive charge. This is because more protons in the nucleus pull the electrons closer, reducing the size of the ion.

3. **Examine Potassium and Calcium**:
- Potassium (K) has an atomic number of 19 and forms K⁺ with a +1 charge.
- Calcium (Ca) has an atomic number of 20 and forms Ca²⁺ with a +2 charge.
- The ionic radius of K⁺ is larger than that of Ca²⁺ because K⁺ has one less positive charge, resulting in less nuclear attraction on its outer electrons.

4. **Examine Transition Metals**:
- Transition metals like Manganese (Mn) and Iron (Fe) have ionic forms Mn²⁺ and Fe²⁺, respectively.
- The difference in ionic radii between these transition metals is relatively small because they have similar charges and their d-orbitals do not significantly affect the size.

5. **Compare the Differences**:
- The difference in ionic radii between K⁺ and Ca²⁺ is significant due to the different charges and their positions in the periodic table.
- In contrast, the difference between the ionic radii of transition metals like Mn²⁺ and Fe²⁺ is minimal.

6. **Conclusion**:
- Therefore, the pair with the maximum difference in ionic radii is Potassium (K) and Calcium (Ca).

### Final Answer:
The two metals with the maximum difference between their ionic radii are Potassium (K) and Calcium (Ca).