When the atoms `Li,Be,B` and `Na` are arranged in order of increasing atomic radius, what is the correct order?

Options

A. `B, Be, Li, Na`
B. `Li, Be, B, Na`
C. `Be, Li, B, Na`
D. `Be,B, Li, Na`

Answer

To determine the order of increasing atomic radius for the elements lithium (Li), beryllium (Be), boron (B), and sodium (Na), we can follow these steps:

### Step 1: Understand the periodic trends
- Atomic radius generally decreases as you move from left to right across a period in the periodic table due to an increase in effective nuclear charge.
- Atomic radius increases as you move down a group because additional electron shells are added, increasing the distance between the nucleus and the outermost electrons.

### Step 2: Identify the positions of the elements
- Lithium (Li) is in Group 1, Period 2.
- Beryllium (Be) is in Group 2, Period 2.
- Boron (B) is in Group 13, Period 2.
- Sodium (Na) is in Group 1, Period 3.

### Step 3: Compare the elements
- Since Li, Be, and B are in the same period (Period 2), we can compare their atomic radii directly. According to the trend, as we move from Li to Be to B, the atomic radius decreases.
- Sodium (Na), being in Period 3, will have a larger atomic radius compared to the elements in Period 2.

### Step 4: Arrange in order of increasing atomic radius
- Based on the trends:
- Boron (B) has the smallest atomic radius.
- Beryllium (Be) is next.
- Lithium (Li) follows.
- Sodium (Na) has the largest atomic radius.

Thus, the order of increasing atomic radius is:
**B < Be < Li < Na**

### Final Answer
The correct order of increasing atomic radius for the elements Li, Be, B, and Na is:
**B < Be < Li < Na**