Define ionisation enthalpy .Discuss the factors affecting ionisation enthalpy of the element and its trends in the periodic table.

Explanation

### Step-by-Step Solution:

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

**Step 2: Discuss Factors Affecting Ionization Enthalpy**
Several factors influence the ionization enthalpy of an element:

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