The property of halogens which is not correctly matched is

Options

A. `F gt Cl gt Br gt I" "`(Ionisation energy)
B. `F gt Cl gt Br gt I" "` (Electronegativity)
C. `I gt Br gt Cl gt F" "` (Density)
D. `F gt Cl gt Br gt I" "` (Electron affinity)

Explanation

To determine which property of halogens is not correctly matched, we will analyze the properties of halogens based on the given options. The properties we will examine include ionization energy, electronegativity, density, and electron affinity.

### Step-by-Step Solution:

1. **Ionization Energy**:
- Ionization energy refers to the energy required to remove an electron from an atom.
- In the group of halogens (Group 17), ionization energy decreases as we move down the group from fluorine (F) to iodine (I).
- Therefore, fluorine has the highest ionization energy, while iodine has the lowest.
- **Conclusion**: The trend for ionization energy is correctly matched.

2. **Electronegativity**:
- Electronegativity is the tendency of an atom to attract electrons in a chemical bond.
- Similar to ionization energy, electronegativity decreases down the group from fluorine to iodine.
- Fluorine is the most electronegative element, while iodine is the least.
- **Conclusion**: The trend for electronegativity is correctly matched.

3. **Density**:
- Density of halogens increases as we move down the group from fluorine to iodine.
- Thus, fluorine has the lowest density, followed by chlorine, bromine, and finally iodine, which has the highest density.
- **Conclusion**: The trend for density is correctly matched.

4. **Electron Affinity**:
- Electron affinity is the energy change that occurs when an electron is added to a neutral atom.
- For halogens, the trend is that electron affinity generally decreases down the group.
- However, fluorine has a lower electron affinity than chlorine due to its small size, which leads to electron-electron repulsion when an additional electron is added.
- The correct trend is that chlorine has a higher electron affinity than fluorine, which contradicts the statement in the options.
- **Conclusion**: The trend for electron affinity is not correctly matched.

### Final Answer:
The property of halogens which is not correctly matched is **electron affinity**.