Which of the following represent the correct order of increasing first ionisation enthalpy for `Ca,Ba,S,Se` and `Ar`

Options

A. `S lt Se lt Ca lt Ba lt Ar`
B. `Ba lt Ca lt Se lt S lt Ar`
C. `Ca lt Ba lt S lt Se 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 Calcium (Ca), Barium (Ba), Sulfur (S), Selenium (Se), and Argon (Ar), we need to analyze their positions in the periodic table and apply the trends of ionization enthalpy.

### Step 1: Understanding Ionization Enthalpy
Ionization enthalpy is the energy required to remove the most loosely bound electron from an isolated gaseous atom. The first ionization enthalpy refers to the energy needed to remove the first electron.

### Step 2: Periodic Trends
1. **Across a Period**: Ionization enthalpy increases across a period due to the increase in effective nuclear charge, which pulls electrons closer to the nucleus, making them harder to remove.
2. **Down a Group**: Ionization enthalpy decreases down a group because the number of electron shells increases, resulting in a greater distance between the nucleus and the outermost electrons, making them easier to remove.

### Step 3: Analyzing the Given Elements
- **Argon (Ar)**: A noble gas with a complete outer shell, it has the highest ionization enthalpy because it is very stable and does not easily lose electrons.
- **Sulfur (S)**: A non-metal in period 3, it has a higher ionization enthalpy than the metals below it.
- **Selenium (Se)**: A non-metal in period 4, it has a lower ionization enthalpy than sulfur but higher than metals.
- **Calcium (Ca)**: A metal in group 2, period 4, it has a lower ionization enthalpy than sulfur and selenium.
- **Barium (Ba)**: A metal in group 2, period 6, it has the lowest ionization enthalpy among the given elements due to being further down the group.

### Step 4: Arranging the Elements
Based on the analysis:
1. **Lowest Ionization Enthalpy**: Barium (Ba)
2. **Next Lowest**: Calcium (Ca)
3. **Followed by**: Selenium (Se)
4. **Then**: Sulfur (S)
5. **Highest Ionization Enthalpy**: Argon (Ar)

### Final Order
The correct order of increasing first ionization enthalpy is:
**Ba < Ca < Se < S < Ar**

### Conclusion
Thus, the correct option representing the increasing order of first ionization enthalpy for the elements Ca, Ba, S, Se, and Ar is:
**Barium < Calcium < Selenium < Sulfur < Argon**