The correct order of increasing order of size is

Options

A. `S lt O lt Se lt C `
B. `O lt C lt S lt Se`
C. `O lt Se lt S lt C`
D. `C lt O lt S lt Se `

Answer

To determine the correct order of increasing atomic size for the elements carbon (C), oxygen (O), sulfur (S), and selenium (Se), we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Elements and Their Positions in the Periodic Table**:
- Carbon (C) is in Group 14, Period 2.
- Oxygen (O) is in Group 16, Period 2.
- Sulfur (S) is in Group 16, Period 3.
- Selenium (Se) is in Group 16, Period 4.

2. **Understand the Trend Across a Period**:
- As we move from left to right across a period, the atomic size decreases. This is due to the increase in effective nuclear charge, which pulls the electrons closer to the nucleus.

3. **Understand the Trend Down a Group**:
- As we move down a group, the atomic size increases. This is because additional electron shells are added, which outweighs the increase in nuclear charge.

4. **Compare the Sizes of the Elements**:
- Between Carbon and Oxygen: Oxygen is smaller than Carbon because they are in the same period, and oxygen is further to the right.
- Between Sulfur and Selenium: Selenium is larger than Sulfur because it is in a lower period (Period 4 vs. Period 3).
- Comparing Carbon, Oxygen, Sulfur, and Selenium:
- Oxygen (smallest)
- Carbon
- Sulfur
- Selenium (largest)

5. **Establish the Increasing Order of Size**:
- Based on the above comparisons, we can arrange the elements in order of increasing size:
- O < C < S < Se

### Final Answer:
The correct order of increasing atomic size is: **O < C < S < Se**.