Electronic configuration of four elements A, B ,C and D are given below
A) `1s^(2), 2s^(2), 2p^(6)`
B) `1s^(2), 2s^(2), 2p^(4)`
C) `1s^(2), 2s^(2), 2p^(6), 3s^(1)`
D) `1s^(2), 2s^(2), 2p^(5)`
Which of the following is the correct order of increasing tendency to gain electron?

Options

A. `AltCltBltD`
B. `AltBltCltD`
C. `DltBltCltA`
D. `DltAltBltC`

Explanation

To determine the correct order of increasing tendency to gain electrons for the elements A, B, C, and D based on their electronic configurations, we will analyze each element step by step.

### Step-by-Step Solution:

1. **Identify the Electronic Configurations:**
- A: `1s² 2s² 2p⁶`
- B: `1s² 2s² 2p⁴`
- C: `1s² 2s² 2p⁶ 3s¹`
- D: `1s² 2s² 2p⁵`

2. **Determine the Stability of Each Configuration:**
- Element A has a full outer shell (2p⁶), indicating it is a noble gas (Neon). Noble gases are stable and have the least tendency to gain electrons.
- Element B has 4 electrons in the 2p orbital. It needs 2 more electrons to achieve a stable noble gas configuration (Neon).
- Element C has 1 electron in the 3s orbital. It needs 1 more electron to complete this orbital, but it is less stable than a noble gas configuration.
- Element D has 5 electrons in the 2p orbital. It needs only 1 more electron to achieve a stable noble gas configuration.

3. **Rank the Elements Based on Tendency to Gain Electrons:**
- **Element A**: Least tendency to gain electrons (noble gas configuration).
- **Element C**: Needs 1 electron to fill the 3s orbital, but is less stable than elements needing to fill the 2p orbital.
- **Element B**: Needs 2 electrons to achieve a noble gas configuration, thus has a higher tendency to gain electrons than C.
- **Element D**: Needs only 1 electron to achieve a noble gas configuration, indicating the highest tendency to gain electrons.

4. **Final Order of Increasing Tendency to Gain Electrons:**
- A < C < B < D

### Conclusion:
The correct order of increasing tendency to gain electrons is:
**A < C < B < D**