Which of the following have no unit ?

Options

A. Electronegativity
B. Electron gain enthalpy
C. Ionisation enthalpy
D. Atomic radii

Explanation

To determine which of the following has no unit, we need to analyze the properties mentioned in the question. Let's break down the relevant concepts step by step.

### Step 1: Understand Electronegativity
Electronegativity is defined as the tendency of an atom to attract electrons in a chemical bond. It is a dimensionless quantity, meaning it does not have any units associated with it.

### Step 2: Understand Electron Gain Enthalpy
Electron gain enthalpy refers to the amount of energy released when an electron is added to a neutral atom in the gaseous state. This process involves energy changes that are measurable and thus has units, typically expressed in kilojoules per mole (kJ/mol).

### Step 3: Understand Ionization Enthalpy
Ionization enthalpy is the energy required to remove an electron from a neutral atom in the gaseous state. Like electron gain enthalpy, ionization enthalpy is also measurable and has units, usually in kilojoules per mole (kJ/mol).

### Step 4: Conclusion
From the analysis:
- Electronegativity is unitless.
- Electron gain enthalpy has units (kJ/mol).
- Ionization enthalpy has units (kJ/mol).

Thus, the property that has no unit is **Electronegativity**.

### Final Answer:
**Electronegativity has no unit.**

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