One among the following is the incrorrect order of increasing ionisation energy :

Options

A. `Cl- gt Ar gt K^+`
B. `Klt Calt Se`
C. `Au lt Ag lt Cu `
D. `Cs lt Rb lt K`

Explanation

To solve the question regarding the incorrect order of increasing ionization energy, we will analyze the given options based on the periodic trends of ionization energy.

### Step-by-Step Solution:

1. **Understanding Ionization Energy**:
- Ionization energy is the energy required to remove an electron from an atom in its gaseous state.
- It generally increases across a period (from left to right) due to the increase in nuclear charge and decreases down a group (from top to bottom) due to the increase in atomic size.

2. **Analyzing the Options**:
- We need to evaluate each given order of elements in terms of their ionization energy.

3. **Option 1**: Chlorine (Cl⁻), Argon (Ar), Potassium (K⁺)
- **Size Order**: K⁺ > Cl⁻ > Ar (K⁺ is the largest, Cl⁻ is smaller than K⁺, and Ar is the smallest).
- **Ionization Energy Order**: K⁺ < Cl⁻ < Ar (Ionization energy increases as size decreases).
- This order is correct.

4. **Option 2**: Potassium (K), Calcium (Ca), Calcium (Ca)
- **Size Order**: K > Ca (K is larger than Ca).
- **Ionization Energy Order**: K < Ca (Ionization energy increases as size decreases).
- This order is correct.

5. **Option 3**: Copper (Cu), Silver (Ag), Gold (Au)
- **Size Order**: Cu < Ag < Au (Size increases down the group).
- **Ionization Energy Order**: Cu > Ag > Au (Cu has the highest ionization energy, followed by Ag, then Au).
- However, due to the presence of the f-orbitals in Au, it has a higher ionization energy than Ag, making this order incorrect. The correct order should be Cu > Au > Ag.

6. **Option 4**: Potassium (K), Rubidium (Rb), Cesium (Cs)
- **Size Order**: K > Rb > Cs (Size increases down the group).
- **Ionization Energy Order**: K > Rb > Cs (Ionization energy decreases as size increases).
- This order is correct.

7. **Conclusion**:
- The incorrect order of increasing ionization energy is found in Option 3: Copper (Cu), Silver (Ag), Gold (Au).

### Final Answer:
The incorrect order of increasing ionization energy is **Copper (Cu), Silver (Ag), Gold (Au)**.

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