The correct order of increasing atomic radius of the following elements as:

Options

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

Answer

To determine the correct order of increasing atomic radius for the given elements (carbon, oxygen, sulfur, and selenium), we can follow these steps:

### Step 1: Identify the Group and Period of Each Element
- **Carbon (C)**: Group 14, Period 2
- **Oxygen (O)**: Group 16, Period 2
- **Sulfur (S)**: Group 16, Period 3
- **Selenium (Se)**: Group 16, Period 4

### Step 2: Understand the Trends in Atomic Radius
- **Down a Group**: Atomic radius increases as you move down a group due to the addition of electron shells, which outweighs the increase in nuclear charge.
- **Across a Period**: Atomic radius decreases as you move from left to right across a period due to an increase in nuclear charge, which pulls the electrons closer to the nucleus.

### Step 3: Compare the Elements
- **Carbon (C)**: Being in Period 2 and Group 14, it has a smaller atomic radius compared to elements in lower periods.
- **Oxygen (O)**: Also in Period 2 but in Group 16, it has a smaller atomic radius than sulfur and selenium but larger than carbon.
- **Sulfur (S)**: In Period 3 and Group 16, it has a larger atomic radius than both carbon and oxygen.
- **Selenium (Se)**: In Period 4 and Group 16, it has the largest atomic radius among the four elements.

### Step 4: Arrange the Elements in Order of Increasing Atomic Radius
Based on the above comparisons:
1. Carbon (C) - smallest atomic radius
2. Oxygen (O)
3. Sulfur (S)
4. Selenium (Se) - largest atomic radius

Thus, the order of increasing atomic radius is:
**C < O < S < Se**

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

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