The first ionization enthalpy of the following elements are in the order :

Options

A. `C lt N lt Si lt P`
B. `P lt Si lt N lt C`
C. `P lt Si lt C lt N`
D. `Si lt P lt C lt N`

Explanation

To determine the order of the first ionization enthalpy of the elements Carbon (C), Nitrogen (N), Phosphorus (P), and Silicon (Si), we will analyze their electronic configurations, stability, and trends in ionization energy.

### Step-by-Step Solution:

1. **Understanding Ionization Enthalpy**:
- Ionization enthalpy is the energy required to remove the outermost electron from a gaseous atom. Higher ionization enthalpy means that more energy is needed to remove the electron, indicating a more stable atom.

2. **Identify Electronic Configurations**:
- Carbon (C): 1s² 2s² 2p²
- Nitrogen (N): 1s² 2s² 2p³
- Silicon (Si): 1s² 2s² 2p⁶ 3s² 3p²
- Phosphorus (P): 1s² 2s² 2p⁶ 3s² 3p³

3. **Trends in Ionization Energy**:
- Ionization energy generally increases across a period (left to right) due to increasing nuclear charge and decreasing atomic size.
- Ionization energy decreases down a group due to increasing atomic size and shielding effect.

4. **Comparing Elements**:
- **Nitrogen (N)** has a half-filled p subshell (2p³), which is particularly stable and will have the highest ionization energy.
- **Carbon (C)** has a less stable configuration compared to nitrogen but is still more stable than silicon and phosphorus due to its smaller size.
- **Phosphorus (P)** has a half-filled p subshell (3p³) but is larger than nitrogen, leading to lower ionization energy than nitrogen but higher than silicon.
- **Silicon (Si)**, being larger than carbon and phosphorus, will have the lowest ionization energy among these four elements.

5. **Order of Ionization Enthalpy**:
- Based on the above analysis, the order of first ionization enthalpy from lowest to highest is:
- Silicon (Si) < Phosphorus (P) < Carbon (C) < Nitrogen (N)

### Final Answer:
The order of first ionization enthalpy is:
**Si < P < C < N**