In the following questions a statement of assertion (A) is followed by a statement of reason ( R)
A : Atomic radii decreases in a period upto halogen .
R : van der Waal radii of CI is larger than its covalent radii.

Options

A. If Both Assertion & Reason are true and the reason is the correct explanation of the assertion then mark (1) .
B. If both Assertion & Reason are true but the reason is not the correct explanation of the assertion then mark (2)
C. If Assertion is true statement but Reason is false then mark (3)
D. If both Assertion and Reason are false statements then mark (4)

Answer

To solve the question regarding the assertion (A) and reason (R), we will analyze both statements step by step.

### Step 1: Analyze the Assertion (A)
The assertion states: "Atomic radii decreases in a period up to halogen."

- **Explanation**: As we move from left to right across a period in the periodic table, the atomic number increases, which means the number of protons in the nucleus increases. This results in a stronger positive charge that pulls the electrons closer to the nucleus, leading to a decrease in atomic radius. This trend continues until we reach the halogens (Group 17), where the atomic radius is at its minimum for that period.

### Step 2: Analyze the Reason (R)
The reason states: "Van der Waals radii of Cl is larger than its covalent radii."

- **Explanation**: The Van der Waals radius refers to the size of an atom when it is not bonded to another atom, while the covalent radius refers to the size of an atom when it is bonded to another atom. For chlorine (Cl), it is true that the Van der Waals radius is larger than its covalent radius. However, this statement is not directly relevant to the assertion about atomic radii decreasing in a period.

### Step 3: Determine the Truth Value of Both Statements
- The assertion (A) is **true** because atomic radii do decrease across a period up to halogens.
- The reason (R) is **true** as well, since the Van der Waals radius of chlorine is indeed larger than its covalent radius.

### Step 4: Evaluate the Relationship Between A and R
- The reason provided does not explain the assertion. While both statements are true, the reason does not provide a rationale for why atomic radii decrease in a period.

### Conclusion
Based on the analysis:
- Both assertion (A) and reason (R) are true, but the reason is not the correct explanation of the assertion.

### Final Answer
The correct option is **2**: Both assertion and reason are true, but the reason is not the correct explanation of the assertion.