Assertion: Potassium has a bigger atomic radius than Lithium
Reason :Atomic radius decreases along a period

Options

A. Both A and R are true and R is correct explanation of the assertion.
B. Both A and R are true but R is not the correct explanation of the assertion.
C. A is true but R is false.
D. A is false but R is true.

Explanation

To solve the question, we need to analyze the assertion and the reason provided:

**Assertion:** Potassium has a bigger atomic radius than Lithium.
**Reason:** Atomic radius decreases along a period.

### Step-by-Step Solution:

1. **Identify the Group and Period of Elements:**
- Potassium (K) and Lithium (Li) are both alkali metals, located in Group 1 of the periodic table.
- Lithium is in Period 2, while Potassium is in Period 4.

2. **Understand Atomic Radius Trends:**
- Atomic radius generally increases as you move down a group in the periodic table. This is because additional electron shells are added, which increases the distance between the nucleus and the outermost electrons.
- Conversely, atomic radius decreases as you move from left to right across a period due to increasing nuclear charge, which pulls the electrons closer to the nucleus.

3. **Compare Atomic Radii of Lithium and Potassium:**
- Lithium has an atomic radius smaller than that of Potassium. This is because Potassium has more electron shells (4 shells) compared to Lithium (2 shells). Thus, the assertion that Potassium has a bigger atomic radius than Lithium is **true**.

4. **Evaluate the Reason:**
- The reason states that atomic radius decreases along a period. This is also **true**, as explained earlier. As you move from left to right in a period, the effective nuclear charge increases, leading to a decrease in atomic radius.

5. **Determine the Relationship Between Assertion and Reason:**
- While both statements are true, the reason does not explain why Potassium has a larger atomic radius than Lithium. The increase in atomic radius down a group (which explains the assertion) is not addressed by the reason that focuses on the trend across a period.

### Conclusion:
- Both the assertion and reason are true, but the reason is not the correct explanation for the assertion.

### Final Answer:
- Both the assertion and reason are true, but the reason is not the correct explanation for the assertion.

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