The first ionisation energy is maximum for

Options

A. `Na`
B. `Mg`
C. `K`
D. `Kr`

Explanation

To determine which element has the maximum first ionization energy among the given options (sodium, magnesium, potassium, and krypton), we can follow these steps:

### Step 1: Understand Ionization Energy
Ionization energy is the energy required to remove an electron from an atom in its gaseous state. Generally, ionization energy increases across a period and decreases down a group in the periodic table.

### Step 2: Analyze Each Element
1. **Sodium (Na)**: Sodium is an alkali metal (Group 1). Alkali metals have low ionization energies because they have a single electron in their outermost shell, which is relatively easy to remove.

2. **Magnesium (Mg)**: Magnesium is an alkaline earth metal (Group 2). It has a higher ionization energy than sodium because it has two electrons in its outer shell, making it slightly more difficult to remove an electron compared to sodium.

3. **Potassium (K)**: Potassium is also an alkali metal (Group 1) and is below sodium in the periodic table. Being lower in the group, it has a larger atomic radius, which results in a lower ionization energy compared to sodium.

4. **Krypton (Kr)**: Krypton is a noble gas (Group 18). Noble gases have a complete outer electron shell, making them very stable and requiring a significant amount of energy to remove an electron. Therefore, krypton has a very high ionization energy.

### Step 3: Compare Ionization Energies
Based on the analysis:
- Potassium < Sodium < Magnesium < Krypton

### Conclusion
The element with the maximum first ionization energy among the given options is **Krypton (Kr)**.

### Final Answer
Krypton has the maximum first ionization energy.

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