Among which of these element pairs is the increase in radius minimum?

Options

A. Li to Na
B. Na to K
C. K to Rb
D. Rb to Cs

Answer

To determine among the given pairs of elements where the increase in atomic radius is minimum, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Trend in Atomic Radius**:
- Atomic radius generally decreases across a period (from left to right) due to increased nuclear charge attracting the electrons closer to the nucleus.
- Atomic radius increases down a group (from top to bottom) due to the addition of electron shells.

2. **Identify the Element Pairs**:
- The pairs mentioned in the question are:
- Lithium (Li) and Sodium (Na)
- Sodium (Na) and Potassium (K)
- Potassium (K) and Rubidium (Rb)
- Rubidium (Rb) and Cesium (Cs)

3. **Gather Atomic Radius Values**:
- From the video transcript, the atomic radius values in picometers (pm) are:
- Lithium (Li): 152 pm
- Sodium (Na): 154 pm
- Potassium (K): 196 pm
- Rubidium (Rb): 211 pm
- Cesium (Cs): 225 pm

4. **Calculate the Increase in Radius for Each Pair**:
- **Li to Na**: 154 pm - 152 pm = 2 pm
- **Na to K**: 196 pm - 154 pm = 42 pm
- **K to Rb**: 211 pm - 196 pm = 15 pm
- **Rb to Cs**: 225 pm - 211 pm = 14 pm

5. **Compare the Increases**:
- The increases in atomic radius are:
- Li to Na: 2 pm
- Na to K: 42 pm
- K to Rb: 15 pm
- Rb to Cs: 14 pm

6. **Determine the Minimum Increase**:
- The smallest increase in atomic radius is from Lithium to Sodium, which is 2 pm.

### Conclusion:
The increase in atomic radius is minimum between Lithium (Li) and Sodium (Na).

---