Arrange the following in order of increasing atomic radii Na, Si, Al, Ar :

Options

A. Na lt Si lt Al lt Ar
B. ` Si lt Al lt Na lt Ar`
C. Ar lt Al lt Si lt Na
D. Na lt Al lt Si lt Ar

Answer

To arrange the elements Na (Sodium), Si (Silicon), Al (Aluminum), and Ar (Argon) in order of increasing atomic radii, we can follow these steps:

### Step 1: Identify the Atomic Numbers and Electronic Configurations
- **Na (Sodium)**: Atomic number = 11, Electronic configuration = 1s² 2s² 2p⁶ 3s¹
- **Si (Silicon)**: Atomic number = 14, Electronic configuration = 1s² 2s² 2p⁶ 3s² 3p²
- **Al (Aluminum)**: Atomic number = 13, Electronic configuration = 1s² 2s² 2p⁶ 3s² 3p¹
- **Ar (Argon)**: Atomic number = 18, Electronic configuration = 1s² 2s² 2p⁶ 3s² 3p⁶

### Step 2: Determine the Group and Period of Each Element
- **Na**: Group 1 (S-block), Period 3
- **Si**: Group 14 (P-block), Period 3
- **Al**: Group 13 (P-block), Period 3
- **Ar**: Group 18 (Noble gas), Period 3

### Step 3: Understand the Trend of Atomic Radii
- Atomic radii generally **decrease across a period** from left to right due to the increase in effective nuclear charge, which pulls the electrons closer to the nucleus.
- Atomic radii generally **increase down a group** due to the addition of electron shells.

### Step 4: Arrange the Elements Based on Atomic Radii
- Since we are looking at elements in the same period (Period 3), we can arrange them based on their position in the periodic table:
- **Na** (Group 1) has the largest atomic radius.
- **Al** (Group 13) is smaller than Na but larger than Si.
- **Si** (Group 14) is smaller than Al.
- **Ar** (Group 18) has the smallest atomic radius due to its fully filled electron shell and increased effective nuclear charge.

### Step 5: Final Order of Increasing Atomic Radii
Thus, the order of increasing atomic radii is:
1. Si (Silicon)
2. Al (Aluminum)
3. Na (Sodium)
4. Ar (Argon)

### Final Answer:
**Si < Al < Na < Ar**