The first ionisation potential of `Na,Mg,Al` and `Si` are in the order

Options

A. `Na lt Mg gt AI lt Si`
B. `Na gt Mg gt AI gt Si`
C. `Na lt Mg lt AI lt Si`
D. `Na gt Mg gt AI gt Si`

Explanation

To determine the order of first ionization potentials of Sodium (Na), Magnesium (Mg), Aluminium (Al), and Silicon (Si), we will analyze their electronic configurations and the trends in ionization energy across the periodic table.

### Step-by-Step Solution:

1. **Identify the Atomic Numbers and Electronic Configurations**:
- Sodium (Na) has an atomic number of 11 and its electronic configuration is:
\[ \text{Na: } 1s^2 2s^2 2p^6 3s^1 \]
- Magnesium (Mg) has an atomic number of 12 and its electronic configuration is:
\[ \text{Mg: } 1s^2 2s^2 2p^6 3s^2 \]
- Aluminium (Al) has an atomic number of 13 and its electronic configuration is:
\[ \text{Al: } 1s^2 2s^2 2p^6 3s^2 3p^1 \]
- Silicon (Si) has an atomic number of 14 and its electronic configuration is:
\[ \text{Si: } 1s^2 2s^2 2p^6 3s^2 3p^2 \]

2. **Understand the Trend in Ionization Energy**:
- Ionization energy generally increases across a period from left to right due to the increase in effective nuclear charge, which holds the electrons more tightly.
- However, there are exceptions due to stable electronic configurations.

3. **Analyze the Ionization Energies**:
- Sodium has one electron in its outermost shell (3s¹), which is relatively easy to remove, resulting in a lower ionization energy.
- Magnesium has a stable configuration with a fully filled 3s subshell (3s²), making it more stable and requiring more energy to remove an electron compared to Sodium.
- Aluminium has one electron in the 3p subshell (3p¹), which is easier to remove than the two electrons in the 3s subshell of Magnesium.
- Silicon has two electrons in the 3p subshell (3p²), which requires more energy to remove than Aluminium.

4. **Order the Ionization Energies**:
- Based on the analysis:
- Sodium (Na) has the lowest ionization energy.
- Aluminium (Al) has a higher ionization energy than Sodium but lower than Magnesium.
- Magnesium (Mg) has a higher ionization energy than Aluminium due to its stable configuration.
- Silicon (Si) has the highest ionization energy among these elements.
- Therefore, the order of first ionization potentials is:
\[ \text{Si} > \text{Mg} > \text{Al} > \text{Na} \]

### Final Answer:
The first ionization potential of Na, Mg, Al, and Si are in the order:
\[ \text{Si} > \text{Mg} > \text{Al} > \text{Na} \]