In the periodic table, the ionisation potential in a group…..from top to bottom

Options

A. increases
B. decreases
C. does not change
D. can not be predicted

Explanation

**Step-by-Step Solution:**

1. **Understanding Ionization Potential:**
- Ionization potential (or ionization energy) is defined as the minimum amount of energy required to remove a valence electron from the valence shell of an isolated gaseous atom.

2. **Electron Removal and Atomic Structure:**
- When we remove an electron, it is taken from the outermost shell (valence shell). The energy required for this removal depends on the attraction between the nucleus and the electron.

3. **Influence of Atomic Size:**
- The size of an atom plays a crucial role in determining ionization potential. As the atomic size increases, the distance between the nucleus and the valence electron also increases, resulting in a weaker attraction.

4. **Trends in Ionization Potential within a Group:**
- As we move down a group in the periodic table, an additional electron shell is added for each successive element. This increase in size leads to a decrease in the effective nuclear charge (Z effective) experienced by the valence electrons.

5. **Conclusion on Ionization Potential:**
- Since the attraction between the nucleus and the valence electrons decreases with increasing atomic size, the energy required to remove the valence electron (ionization potential) also decreases. Therefore, ionization potential decreases from top to bottom in a group.

**Final Answer:**
In the periodic table, the ionization potential decreases from top to bottom in a group.

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