Elements with their electronic configuration are given below:
Answer the following questions: II: `1s^(2) 2s^(2) 2p^(6)`
III: `1s^(2) 2s^(2) 2p^(6)3s^(2)`
IV `1s^(2)2s^(2)2p^(3)`
V: `1s^(2)2s^(2)2p^(5)`
Q. The element with lowest electron gain enthalpy is:

Options

A. I
B. II
C. III
D. IV

Answer

To determine the element with the lowest electron gain enthalpy from the given electronic configurations, we need to analyze each configuration step by step.

### Step 1: Identify the Elements
1. **I: `1s^2 2s^2`** - This configuration corresponds to Beryllium (Be).
2. **II: `1s^2 2s^2 2p^6`** - This configuration corresponds to Neon (Ne).
3. **III: `1s^2 2s^2 2p^6 3s^2`** - This configuration corresponds to Magnesium (Mg).
4. **IV: `1s^2 2s^2 2p^3`** - This configuration corresponds to Phosphorus (P).
5. **V: `1s^2 2s^2 2p^5`** - This configuration corresponds to Chlorine (Cl).

### Step 2: Understand Electron Gain Enthalpy
Electron gain enthalpy refers to the energy change when an electron is added to a neutral gaseous atom to form a negative ion. A more negative value indicates a greater tendency to gain an electron.

### Step 3: Analyze Each Element
- **Beryllium (Be)**: Has a full 2s subshell and does not readily gain an electron, hence it has a low electron gain enthalpy.
- **Neon (Ne)**: Has a complete octet (1s² 2s² 2p⁶) and is very stable, making it unlikely to gain an electron. It has the lowest tendency to gain an electron, resulting in a very low (or positive) electron gain enthalpy.
- **Magnesium (Mg)**: Similar to Be, it has a filled 3s subshell and does not favor gaining an electron.
- **Phosphorus (P)**: Has a half-filled p subshell (2p³), which can gain an electron but is less stable than a noble gas configuration.
- **Chlorine (Cl)**: Has 2p⁵ and can easily gain an electron to achieve a stable octet, resulting in a more negative electron gain enthalpy compared to the others.

### Step 4: Conclusion
Among these elements, **Neon (Ne)** has the lowest electron gain enthalpy because it is already stable with a complete octet and does not favor gaining an electron.

### Final Answer
The element with the lowest electron gain enthalpy is **Neon (Ne)**.

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