Define ionization enthalpy . What are its units ? What is the principle of its measurement ?

Explanation

### Step-by-Step Solution:

**Step 1: Definition of Ionization Enthalpy**
- Ionization enthalpy (or ionization energy) is defined as the minimum amount of energy required to remove an electron from an isolated gaseous atom. This process results in the formation of a positively charged ion.

**Step 2: Units of Ionization Enthalpy**
- Ionization enthalpy can be expressed in several units:
- Electron volts per atom (eV/atom)
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