Which of the following are correct about Zn,Cd,Hg
I) They exhibit enthalpy of atomisation as the d-subshell is full
II) Zn,Cd do not show variable oxidation states, Hg can show +1,+2 states
III) Compounds of `Zn,Cd,Hg` are paramagnetic
IV) They are soft metals

Options

A. I, II, III
B. I, III
C. II, IV
D. IV only

Answer

To determine which statements about Zn, Cd, and Hg are correct, let's analyze each statement step by step.

### Step 1: Analyze the Electronic Configuration
- **Zinc (Zn)**: [Ar] 3d^10 4s^2
- **Cadmium (Cd)**: [Kr] 4d^10 5s^2
- **Mercury (Hg)**: [Xe] 4f^14 5d^10 6s^2

All three elements have completely filled d-subshells (3d^10, 4d^10, and 5d^10).

### Step 2: Evaluate Statement I
**Statement I**: They exhibit enthalpy of atomization as the d-subshell is full.
- Since the d-subshell is completely filled, there are no unpaired electrons, leading to weaker metallic bonding. Therefore, the enthalpy of atomization is lower, not higher.
- **Conclusion**: This statement is **incorrect**.

### Step 3: Evaluate Statement II
**Statement II**: Zn and Cd do not show variable oxidation states, Hg can show +1, +2 states.
- Zinc and cadmium typically exhibit a +2 oxidation state, while mercury can exhibit both +1 and +2 oxidation states.
- **Conclusion**: This statement is **correct**.

### Step 4: Evaluate Statement III
**Statement III**: Compounds of Zn, Cd, and Hg are paramagnetic.
- Since all three elements have completely filled d-subshells, they do not have unpaired electrons, which means they are diamagnetic, not paramagnetic.
- **Conclusion**: This statement is **incorrect**.

### Step 5: Evaluate Statement IV
**Statement IV**: They are soft metals.
- The presence of completely filled d-subshells results in weaker metallic bonds, making them soft metals.
- **Conclusion**: This statement is **correct**.

### Final Conclusion
The correct statements about Zn, Cd, and Hg are:
- Statement II: Correct
- Statement IV: Correct

Thus, the correct answer is that statements II and IV are correct.

### Summary of Correct Statements
- **Correct Statements**: II and IV
- **Incorrect Statements**: I and III