Ionisation energy is highest for

Options

A. Noble gases
B. Platinum metals
C. Transition elements
D. Inner–transition elements

Explanation

To determine which element has the highest ionization energy, we need to understand the concept of ionization energy and the trends in the periodic table.

### Step-by-Step Solution:

1. **Define Ionization Energy**:
Ionization energy is the energy required to remove an electron from an atom in its gaseous state.

2. **Understand the Periodic Trends**:
- Ionization energy generally increases across a period from left to right. This is due to the increasing nuclear charge, which holds the electrons more tightly.
- Ionization energy generally decreases down a group. This is because the outer electrons are further from the nucleus and are shielded by inner electrons.

3. **Identify Noble Gases**:
Noble gases are located in Group 18 of the periodic table. They have a complete valence shell (ns²np⁶), which makes them very stable and gives them high ionization energies.

4. **Compare Noble Gases with Other Elements**:
Among all the elements, noble gases have the highest ionization energies due to their stable electronic configuration. For example, Helium, Neon, and Argon are noble gases with very high ionization energies.

5. **Conclusion**:
Therefore, the element with the highest ionization energy is a noble gas. Specifically, the first noble gas, which is Helium (He), has the highest ionization energy of all elements.

### Final Answer:
The highest ionization energy is found in the first noble gas, Helium (He).

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