The correct values of ionization enthalpies(in KJ `"mol"^(-1)`) of Si, P, Cl, and S respectively are: a)`786, 1012, 999, 1256` b)`1012, 786, 999, 1256` c)`786, 1012, 1256, 999` d)`786, 999, 1012, 1256`

Options

A. 786, 1012, 999, 1256
B. 1012, 786, 999, 1256,
C. 786, 1012, 1256, 999
D. 786, 999, 1012, 1256

Explanation

To determine the correct values of ionization enthalpies for silicon (Si), phosphorus (P), sulfur (S), and chlorine (Cl), we need to analyze the periodic trends and the specific electronic configurations of these elements.

### Step-by-Step Solution:

1. **Identify the Elements and Their Positions**:
- Silicon (Si) is in Group 14, Period 3.
- Phosphorus (P) is in Group 15, Period 3.
- Sulfur (S) is in Group 16, Period 3.
- Chlorine (Cl) is in Group 17, Period 3.

2. **Understand the Trend of Ionization Enthalpy**:
- Ionization enthalpy generally increases from left to right across a period due to increasing nuclear charge and decreasing atomic size.
- However, there are exceptions due to electron configurations, particularly with half-filled and fully filled orbitals.

3. **Consider the Electron Configurations**:
- Silicon: [Ne] 3s² 3p⁰
- Phosphorus: [Ne] 3s² 3p³ (half-filled p-orbital)
- Sulfur: [Ne] 3s² 3p⁴ (more stable than P)
- Chlorine: [Ne] 3s² 3p⁵ (very high ionization energy due to high nuclear charge)

4. **Order the Elements Based on Ionization Enthalpy**:
- Generally, we would expect the order to be:
- Si < P < S < Cl
- However, due to the stability of half-filled orbitals, sulfur will have a higher ionization enthalpy than phosphorus:
- Si < S < P < Cl

5. **Match the Values with Options**:
- Given values in the options are:
- a) 786, 1012, 999, 1256
- b) 1012, 786, 999, 1256
- c) 786, 1012, 1256, 999
- d) 786, 999, 1012, 1256
- From our ordering Si < S < P < Cl, we can deduce the correct values should be:
- Si (786) < S (999) < P (1012) < Cl (1256)

6. **Select the Correct Option**:
- The only option that matches this order is:
- **Option a: 786, 1012, 999, 1256**

### Final Answer:
The correct values of ionization enthalpies of Si, P, Cl, and S respectively are: **a) 786, 1012, 999, 1256**.