Which of the following statement regarding halogens is/are correct?

Options

A. Ionization energy decreases with increase in atomic number
B. electronegativity decreases with increase in atomic number
C. Electron affinity decreases with increase in atomic number
D. Enthalpy of fusion increses with increase in atomic number

Answer

To determine which statements regarding halogens are correct, we need to analyze each statement based on the properties of halogens (Group 17 elements: fluorine, chlorine, bromine, and iodine).

### Step-by-Step Solution:

1. **Understanding Ionization Energy**:
- **Definition**: Ionization energy is the energy required to remove an electron from an atom.
- **Trend in Halogens**: As we move down the group from fluorine to iodine, the atomic number increases, and the number of electron shells also increases. This leads to increased shielding effect and a decrease in effective nuclear charge felt by the outermost electrons. Therefore, the ionization energy decreases.
- **Conclusion**: The statement "Ionization energy decreases with increase in atomic number" is **correct**.

2. **Understanding Electronegativity**:
- **Definition**: Electronegativity is the ability of an atom to attract electrons towards itself in a bond.
- **Trend in Halogens**: Similar to ionization energy, as we move down the group, the effective nuclear charge decreases due to increased distance of the valence electrons from the nucleus and increased shielding. Thus, electronegativity decreases down the group.
- **Conclusion**: The statement "Electronegativity decreases with increase in atomic number" is **correct**.

3. **Understanding Electron Affinity**:
- **Definition**: Electron affinity is the energy change that occurs when an electron is added to a neutral atom.
- **Trend in Halogens**: As we move down the group, the ability to gain an electron decreases due to the increased atomic size and shielding effect, which reduces the effective nuclear charge. Therefore, electron affinity decreases.
- **Conclusion**: The statement "Electron affinity decreases with increase in atomic number" is **correct**.

4. **Understanding Enthalpy of Fusion**:
- **Definition**: Enthalpy of fusion is the amount of energy required to change a substance from solid to liquid at its melting point.
- **Trend in Halogens**: As we move down the group, the size of the halogen molecules increases, leading to longer bond lengths and weaker van der Waals forces between molecules. Consequently, the enthalpy of fusion decreases.
- **Conclusion**: The statement "Enthalpy of fusion increases with increase in atomic number" is **incorrect**.

### Final Summary:
- The correct statements regarding halogens are:
1. Ionization energy decreases with increase in atomic number (Correct)
2. Electronegativity decreases with increase in atomic number (Correct)
3. Electron affinity decreases with increase in atomic number (Correct)
4. Enthalpy of fusion increases with increase in atomic number (Incorrect)