The first ionisation enthalpy of the elements C,N,P,Si are in the order of

Options

A. `CltNltSiltP`
B. `NltSiltCltP`
C. `SiltPltCltN`
D. `PltSiltNltC`

Answer

To determine the order of first ionization enthalpy for the elements carbon (C), nitrogen (N), phosphorus (P), and silicon (Si), we will analyze the periodic trends and properties of these elements.

### Step-by-Step Solution:

1. **Understanding Ionization Enthalpy**:
- Ionization enthalpy (or ionization energy) is the energy required to remove an electron from an isolated gaseous atom in its ground state. Higher ionization enthalpy means it is harder to remove an electron.

2. **Identifying Groups and Periods**:
- Carbon (C) and Silicon (Si) are in Group 14 (IV A).
- Nitrogen (N) and Phosphorus (P) are in Group 15 (V A).
- C and N are in the second period, while Si and P are in the third period.

3. **Trends in Ionization Energy**:
- **Across a Period**: Ionization energy generally increases as you move from left to right across a period due to increasing nuclear charge (more protons) which pulls electrons closer to the nucleus.
- **Down a Group**: Ionization energy generally decreases as you move down a group because the outermost electrons are further from the nucleus and are shielded by inner electrons, making them easier to remove.

4. **Comparing the Elements**:
- **Nitrogen (N)**: Highest ionization energy among the four because it is the furthest to the right in its period.
- **Carbon (C)**: Has a higher ionization energy than silicon and phosphorus because it is above them in the periodic table.
- **Phosphorus (P)**: Lower ionization energy than carbon and nitrogen, but higher than silicon due to its position in the periodic table.
- **Silicon (Si)**: Lowest ionization energy among the four because it is further down in the group.

5. **Final Order**:
- Based on the above analysis, the order of first ionization enthalpy for the elements C, N, P, and Si is:
**N > C > P > Si**

### Conclusion:
The first ionization enthalpy of the elements C, N, P, Si is in the order of:
**N > C > P > Si**