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

Options

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

Explanation

To determine the order of the first ionization potentials of sodium (Na), magnesium (Mg), aluminum (Al), and silicon (Si), we will follow these steps:

### Step 1: Write the Electronic Configurations
- **Sodium (Na)**: Atomic number = 11
- Electronic Configuration: \(1s^2 2s^2 2p^6 3s^1\)

- **Magnesium (Mg)**: Atomic number = 12
- Electronic Configuration: \(1s^2 2s^2 2p^6 3s^2\)

- **Aluminum (Al)**: Atomic number = 13
- Electronic Configuration: \(1s^2 2s^2 2p^6 3s^2 3p^1\)

- **Silicon (Si)**: Atomic number = 14
- Electronic Configuration: \(1s^2 2s^2 2p^6 3s^2 3p^2\)

### Step 2: Analyze the Position in the Periodic Table
- All four elements are in the third period of the periodic table.
- As we move from left to right across a period, the ionization potential generally increases due to the increasing nuclear charge which holds the electrons more tightly.

### Step 3: Compare Ionization Energies
- **Sodium (Na)** has one electron in its outermost shell (3s^1), making it easier to remove, hence it has the lowest ionization potential.
- **Magnesium (Mg)** has a completely filled outer shell (3s^2), which makes it more stable and requires more energy to remove an electron compared to sodium.
- **Aluminum (Al)** has three electrons in its outer shell (3s^2 3p^1). Removing one of these electrons is easier than removing an electron from magnesium but harder than sodium.
- **Silicon (Si)** has four electrons in its outer shell (3s^2 3p^2), making it harder to remove an electron than from aluminum.

### Step 4: Establish the Order of Ionization Potentials
Based on the analysis:
- **Lowest Ionization Potential**: Sodium (Na)
- **Next**: Aluminum (Al)
- **Next**: Silicon (Si)
- **Highest Ionization Potential**: Magnesium (Mg)

Thus, the order of first ionization potentials is:
\[ \text{Na} < \text{Al} < \text{Si} < \text{Mg} \]

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