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. Which of the following is the correct order of increasing size?

Options

A. `I lt III lt IV lt V`
B. `V lt IV lt III lt I`
C. `I lt IV lt V lt III`
D. `V lt IV lt I lt III`

Answer

To determine the correct order of increasing atomic size for the given elements based on their electronic configurations, we will analyze the atomic numbers and the trends in atomic size.

### Step-by-Step Solution:

1. **Identify the Elements and Their Atomic Numbers**:
- I: `1s^2 2s^2` → Beryllium (Be), Atomic Number = 4
- II: `1s^2 2s^2 2p^6` → Neon (Ne), Atomic Number = 10
- III: `1s^2 2s^2 2p^6 3s^2` → Magnesium (Mg), Atomic Number = 12
- IV: `1s^2 2s^2 2p^3` → Nitrogen (N), Atomic Number = 7
- V: `1s^2 2s^2 2p^5` → Fluorine (F), Atomic Number = 9

2. **Determine the Size Trend**:
- Atomic size generally increases down a group due to the addition of electron shells.
- Atomic size generally decreases across a period from left to right due to increased nuclear charge pulling the electrons closer to the nucleus.

3. **Order the Elements by Atomic Number**:
- Beryllium (Be) = 4
- Nitrogen (N) = 7
- Fluorine (F) = 9
- Neon (Ne) = 10
- Magnesium (Mg) = 12

4. **Analyze the Sizes**:
- Beryllium has the smallest size because it is the least electronegative and has fewer electron shells compared to the others.
- Magnesium has the largest size due to its higher atomic number and additional electron shell.
- Between Nitrogen, Fluorine, and Neon, the size decreases as we move from Nitrogen to Fluorine to Neon.

5. **Establish the Order of Increasing Size**:
- The correct order of increasing size based on the above analysis is:
- Neon (smallest) < Fluorine < Nitrogen < Beryllium < Magnesium (largest)

### Final Order of Increasing Size:
**Neon < Fluorine < Nitrogen < Beryllium < Magnesium**