Largest difference in radii is found in case of the pair

Options

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

Explanation

To solve the question regarding the largest difference in radii among alkali metals, we can follow these steps:

### Step 1: Identify the Elements
We are given a group of alkali metals: lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs).

### Step 2: Understand the Trend in Radii
Alkali metals are known to increase in size as we move down the group in the periodic table. This is due to the addition of electron shells, which increases the atomic radius.

### Step 3: Gather the Radii Data
From the video transcript, we have the following experimental radii data for the alkali metals:
- Lithium (Li): 152 pm
- Sodium (Na): 180 pm
- Potassium (K): 227 pm
- Rubidium (Rb): 248 pm
- Cesium (Cs): 265 pm

### Step 4: Calculate the Differences in Radii
Now, we will calculate the differences in radii between consecutive alkali metals:
- Difference between Li and Na: 180 - 152 = 28 pm
- Difference between Na and K: 227 - 180 = 47 pm
- Difference between K and Rb: 248 - 227 = 21 pm
- Difference between Rb and Cs: 265 - 248 = 17 pm

### Step 5: Identify the Largest Difference
From the calculated differences:
- Li and Na: 28 pm
- Na and K: 47 pm
- K and Rb: 21 pm
- Rb and Cs: 17 pm

The largest difference is between sodium (Na) and potassium (K), which is 47 pm.

### Conclusion
Thus, the pair with the largest difference in radii is sodium (Na) and potassium (K).

### Final Answer
The correct option is sodium and potassium.

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