`{:("Column A","Column B"),("a. Fluorine"," i. High negative electron gain enthalpy"),("b. Helium"," ii. Most electropositive element"),("c. Chlorine"," iii. Most electronegative element"),("d. Cesium"," iv. Highest ionisation enthalpy"):}`

Answer

To solve the matching question between Column A and Column B, we will analyze each element in Column A and determine the appropriate match from Column B based on their properties.

### Step-by-Step Solution:

1. **Identify the properties of Fluorine:**
- Fluorine is known to be the most electronegative element in the periodic table.
- **Match:** Fluorine (a) → Most electronegative element (iii).

2. **Identify the properties of Helium:**
- Helium is a noble gas and has a complete electron configuration (1s²), which means it has a very high ionization enthalpy because it does not easily lose its electrons.
- **Match:** Helium (b) → Highest ionization enthalpy (iv).

3. **Identify the properties of Chlorine:**
- Chlorine has a high negative electron gain enthalpy because it is relatively large compared to Fluorine and can easily gain an electron to achieve a stable configuration.
- **Match:** Chlorine (c) → High negative electron gain enthalpy (i).

4. **Identify the properties of Cesium:**
- Cesium is located in Group 1 of the periodic table and is the largest alkali metal, making it the most electropositive element.
- **Match:** Cesium (d) → Most electropositive element (ii).

### Final Matches:
- a → iii (Fluorine → Most electronegative element)
- b → iv (Helium → Highest ionization enthalpy)
- c → i (Chlorine → High negative electron gain enthalpy)
- d → ii (Cesium → Most electropositive element)

### Summary of Matches:
- a. Fluorine → iii. Most electronegative element
- b. Helium → iv. Highest ionization enthalpy
- c. Chlorine → i. High negative electron gain enthalpy
- d. Cesium → ii. Most electropositive element

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