Which of the following represents the correct order of increasing first ionization enthalpy for Ca, Ba, S , Se and Ar ?

Options

A. `Ca lt Ba lt S lt Se lt Ar`
B. `S lt Se lt Ca lt Ba lt Ar`
C. `Ba lt Ca lt Se lt S lt Ar`
D. `Ca lt S lt Ba lt Se lt Ar`

Answer

To determine the correct order of increasing first ionization enthalpy for the elements Ca (Calcium), Ba (Barium), S (Sulfur), Se (Selenium), and Ar (Argon), we will analyze the periodic trends and the properties of these elements.

### Step-by-Step Solution:

1. **Understand Ionization Energy**:
- Ionization energy is the energy required to remove an electron from a neutral gaseous atom. The first ionization energy refers to the energy needed to remove the first electron.

2. **Periodic Trends**:
- **Across a Period**: Ionization energy increases as you move from left to right across a period due to increasing nuclear charge and decreasing atomic radius.
- **Down a Group**: Ionization energy decreases as you move down a group because the atomic size increases, making it easier to remove an outer electron.

3. **Identify the Periods of the Elements**:
- Calcium (Ca) is in the 4th period.
- Barium (Ba) is in the 6th period.
- Sulfur (S) is in the 3rd period.
- Selenium (Se) is in the 4th period.
- Argon (Ar) is in the 3rd period.

4. **Rank the Elements Based on Periodic Trends**:
- **Barium (Ba)**: Being in the 6th period, it has the lowest ionization energy due to its larger atomic size.
- **Calcium (Ca)**: Also an alkaline earth metal but in the 4th period, it has a higher ionization energy than Ba.
- **Argon (Ar)**: As a noble gas in the 3rd period, it has a very high ionization energy because it has a stable electron configuration.
- **Sulfur (S)**: In the 3rd period, it has a higher ionization energy than Argon due to its smaller atomic size and higher effective nuclear charge.
- **Selenium (Se)**: In the 4th period, it has a lower ionization energy than Sulfur but higher than Calcium and Barium.

5. **Final Order**:
- Based on the above analysis, the order of increasing first ionization enthalpy is:
- Ba < Ca < Ar < Se < S

### Conclusion:
The correct order of increasing first ionization enthalpy for Ca, Ba, S, Se, and Ar is:
**Ba < Ca < Ar < Se < S**