Name the elements which possess most negative values of electron gain enthalpy in their periods.

Explanation

To answer the question regarding the elements that possess the most negative values of electron gain enthalpy in their periods, we can follow these steps:

### Step 1: Understand Electron Gain Enthalpy
- **Definition**: Electron gain enthalpy is the amount of energy released when an electron is added to a neutral atom. A more negative value indicates that more energy is released, meaning the atom has a stronger tendency to gain an electron.

### Step 2: Identify the Group with Most Negative Electron Gain Enthalpy
- **Halogens**: The elements that exhibit the most negative values of electron gain enthalpy are the halogens. This group includes fluorine (F), chlorine (Cl), bromine (Br), and iodine (I).

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