The incorrect order is :

Options

A. Mn `gt` Fe (Illrd ionisation energy)
B. Cr `gt` Mn (Ilnd lonisation energy)
C. `Cu^(1+)(aq) gt Cu^(2+)(aq)` (stability order)
D. All of these

Answer

To determine the incorrect order from the given options regarding ionization energies and stability of ions, we will analyze each option step by step.

### Step 1: Analyze Option A
**Statement:** The third ionization energy of manganese (Mn) is greater than that of iron (Fe).

- **Manganese (Mn):** Atomic number = 25; Electron configuration = Argon 3d5 4s2.
- After losing 2 electrons (from 4s), it becomes Mn²⁺ with configuration Argon 3d5.
- The third ionization energy involves removing an electron from the stable 3d5 configuration, which requires a significant amount of energy.

- **Iron (Fe):** Atomic number = 26; Electron configuration = Argon 3d6 4s2.
- After losing 2 electrons (from 4s), it becomes Fe²⁺ with configuration Argon 3d6.
- The third ionization energy involves removing an electron from 3d6, which is less stable than 3d5.

**Conclusion for Option A:** The third ionization energy of Mn is indeed greater than that of Fe. This order is correct.

### Step 2: Analyze Option B
**Statement:** The second ionization energy of chromium (Cr) is greater than that of manganese (Mn).

- **Chromium (Cr):** Atomic number = 24; Electron configuration = Argon 3d5 4s1.
- After losing 1 electron, it becomes Cr⁺ with configuration Argon 3d5.
- The second ionization energy involves removing an electron from the stable 3d5 configuration.

- **Manganese (Mn):** As analyzed earlier, after losing 1 electron, it becomes Mn⁺ with configuration Argon 3d5 4s1.
- The second ionization energy involves removing an electron from 4s1, which is less stable than removing from 3d5.

**Conclusion for Option B:** The second ionization energy of Cr is indeed greater than that of Mn. This order is correct.

### Step 3: Analyze Option C
**Statement:** The stability order of Cu⁺ (copper 1 positive) is greater than Cu²⁺ (copper 2 positive) in aqueous solution.

- **Cu⁺:** Tends to be less stable in aqueous solution and can disproportionate to form Cu²⁺ and Cu.
- **Cu²⁺:** Has a higher charge density and greater hydration energy due to its smaller size and higher charge, making it more stable in aqueous solution.

**Conclusion for Option C:** The stability of Cu²⁺ is indeed greater than Cu⁺ in aqueous solution. This order is incorrect.

### Step 4: Analyze Option D
**Statement:** This option is not specified in the transcript but is considered incorrect based on the analysis of previous options.

### Final Conclusion
The incorrect order is found in **Option C**, where it states that the stability of Cu⁺ is greater than Cu²⁺ in aqueous solution.