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 analyze the given statements, let's break down the assertion (A) and reason (R) step by step.

### Step 1: Understanding Assertion (A)
**Assertion (A): Atomic radii decreases in a period up to halogen.**

- As we move from left to right across a period in the periodic table, the atomic number (number of protons) increases.
- With an increase in protons, the positive charge in the nucleus increases, which attracts the electrons more strongly.
- Although electrons are also added as we move across the period, the increase in nuclear charge outweighs the effect of added electron-electron repulsion.
- Therefore, the atomic radius decreases as we move from left to right across a period, reaching a minimum at the halogens.

### Step 2: Understanding Reason (R)
**Reason (R): Van der Waals radii of Cl is larger than its covalent radii.**

- The covalent radius is defined as half the distance between two nuclei of atoms bonded together in a molecule.
- The Van der Waals radius is a measure of the size of an atom that is not bonded to another atom, representing the distance at which the electron clouds of two atoms begin to overlap.
- For chlorine (Cl), when it forms a diatomic molecule (Cl2), the distance between the two nuclei is defined as the covalent radius.
- The Van der Waals radius is larger because it accounts for the space taken by the electron cloud when the atoms are not bonded.
- Thus, it is true that the Van der Waals radius of Cl is larger than its covalent radius.

### Step 3: Evaluating the Statements
- **Assertion (A)** is true: Atomic radii do decrease across a period up to halogens.
- **Reason (R)** is also true: The Van der Waals radius of Cl is indeed larger than its covalent radius.

### Conclusion
Since both the assertion and the reason are true, but the reason does not explain the assertion, the correct answer is that the assertion is true, and the reason is true but does not support the assertion.

### Final Answer
The correct answer is B: Assertion is true, Reason is true, but Reason does not explain Assertion.

---