Which of the following has been arranged in order of increasing bond strength ?

Options

A. `Zn_2^(2+) lt Hg_2^(2+) lt Cd_2^(2+)`
B. `Cd_2^(2+) lt Hg_2^(2+) lt Zn_2^(2+)`
C. `Zn_2^(2+) lt Cd_2^(2+) lt Hg_2^(2+)`
D. `Hg_2^(2+) lt Cd_2^(2+) lt Zn_2^(2+)`

Explanation

To determine the order of increasing bond strength among the given ions (Zn²⁺, Cd²⁺, and Hg²⁺), we can analyze the factors affecting bond strength, particularly focusing on the atomic radii and the effective nuclear charge.

### Step-by-Step Solution:

1. **Understanding the Elements:**
- Zinc (Zn) has an atomic number of 30.
- Cadmium (Cd) has an atomic number of 48.
- Mercury (Hg) has an atomic number of 80.
- All three elements are in the d-block of the periodic table.

2. **Analyzing Atomic Radii:**
- As we move down the group from Zn to Cd to Hg, the atomic radii increase. This is because additional electron shells are added, which increases the distance between the nucleus and the outermost electrons.

3. **Effect of Atomic Radii on Bond Strength:**
- Larger atomic radii generally result in weaker nuclear attraction on the valence electrons. This means that the outermost electrons are held less tightly as we move down the group.

4. **Reactivity and Bond Strength:**
- As the atomic radii increase, the reactivity of the elements also increases. This is due to the outermost electrons being more loosely held and more easily lost.
- Therefore, the bond strength of the ions decreases as we move from Zn²⁺ to Cd²⁺ to Hg²⁺.

5. **Order of Bond Strength:**
- Since bond strength is inversely related to reactivity in this context, we can arrange the ions in order of increasing bond strength:
- Hg²⁺ < Cd²⁺ < Zn²⁺
- This indicates that Zn²⁺ has the strongest bond, followed by Cd²⁺, and Hg²⁺ has the weakest bond.

6. **Conclusion:**
- The correct order of increasing bond strength is:
- Hg²⁺ < Cd²⁺ < Zn²⁺

### Final Answer:
The correct option for the order of increasing bond strength is **Hg²⁺ < Cd²⁺ < Zn²⁺**.