A : If a tetrad axis is passed through the unit cell of NaCl and all ions removed which are touching to tetrad axis then the formula of NaCl becomes `Na_(3)Cl_(4)`.
R : Only one `Na^(+)` is removed not the `Cl^(-)`.

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 problem, we need to analyze the assertion (A) and the reason (R) regarding the changes in the formula of NaCl when a tetrad axis passes through its unit cell. Let's break this down step by step:

### Step 1: Understand the Structure of NaCl
NaCl crystallizes in a face-centered cubic (FCC) structure. In this structure:
- There are 8 Na⁺ ions located at the corners of the cube.
- There are 6 Cl⁻ ions located at the faces of the cube.
- There is 1 Na⁺ ion at the body center.

### Step 2: Identify the Tetrad Axis
A tetrad axis (or tetrahedral axis) in a cubic structure typically refers to an axis that passes through the body center and connects to the midpoints of the edges. When this axis is considered, it affects the ions that are in proximity to it.

### Step 3: Remove Ions Touching the Tetrad Axis
According to the assertion, we need to remove all ions that are touching the tetrad axis:
- From the body center, we remove 1 Na⁺ ion.
- From the corners, we remove 2 Cl⁻ ions (since there are 8 corners, and each corner contributes 1/8 of a Cl⁻ ion).

### Step 4: Calculate the Remaining Ions
After removing the ions:
- Remaining Na⁺ ions:
- Initially, there were 4 Na⁺ ions (1 from the body center and 3 from the edges). After removing 1 Na⁺, we have 3 Na⁺ ions left.

- Remaining Cl⁻ ions:
- Initially, there were 8 Cl⁻ ions (from corners) and 6 from faces. After removing 2 Cl⁻ ions, we have:
- From corners: 8 - 2 = 6 Cl⁻ ions.
- From faces: 6 Cl⁻ ions remain unaffected.
- Total Cl⁻ ions = 6 (from corners) + 6 (from faces) = 12 Cl⁻ ions.

### Step 5: Write the New Formula
The new formula can be represented as:
- Na: 3
- Cl: 12

However, we need to express this in the simplest form:
- The formula can be simplified by dividing both the subscripts by 3:
- Na: 3 / 3 = 1
- Cl: 12 / 3 = 4
- Thus, the simplified formula is Na₁Cl₄, which is not what is stated in the assertion.

### Step 6: Conclusion
The assertion states that the formula becomes Na₃Cl₄, which is incorrect. The reason states that only one Na⁺ is removed and not the Cl⁻, which is also misleading since Cl⁻ ions are indeed removed.

### Final Answer
Both the assertion (A) and the reason (R) are false.

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