Which of the following have no unit?

Options

A. Electronegativity
B. Electron gain enthalpy
C. Ionisation enthalpy
D. Metallic character.

Explanation

To determine which of the following have no unit, we need to analyze each term provided in the question.

1. **Electronegativity**:
- Definition: Electronegativity is a measure of an atom's ability to attract shared electrons to itself.
- Analysis: Since it is a relative measure and does not have a physical dimension, electronegativity is dimensionless and has no unit.

2. **Electron Gain Enthalpy**:
- Definition: This refers to the energy change when an electron is added to a gaseous atom.
- Analysis: Electron gain enthalpy is measured in kilojoules per mole (kJ/mol) because it involves energy changes, so it has a unit.

3. **Enthalpy**:
- Definition: Enthalpy is the total heat content of a system and is often associated with the energy required to remove an electron from an atom.
- Analysis: Similar to electron gain enthalpy, enthalpy is also measured in kilojoules per mole (kJ/mol), so it has a unit.

4. **Metallic Character**:
- Definition: This refers to the ability of an atom to lose electrons to form cations.
- Analysis: Metallic character is a qualitative property and does not have a specific unit associated with it, making it dimensionless.

**Conclusion**:
From the analysis, we can conclude that:
- Electronegativity (A) and Metallic Character (D) have no unit.
- Electron Gain Enthalpy (B) and Enthalpy (C) have units (kJ/mol).

Thus, the answer is **Electronegativity and Metallic Character**.