Assertion: Crystalline solids can cause X-rays to diffract.
Reason: Interatomic distance in crystalline solids is of the order of `0.1nm`.

Options

A. If both the Asseration and Reason are true and reason explains the Assertion :
B. If both the Assertion and Reason are true but reason does ot explain the Assertion :
C. If Assertion is true but reason false
D. If Assertion is false but reason is true

Answer

To analyze the given question, we need to evaluate both the assertion and the reason provided.

### Step 1: Understand the Assertion
The assertion states that "Crystalline solids can cause X-rays to diffract." This is true because crystalline solids have a regular and repeating arrangement of atoms. When X-rays, which have wavelengths on the order of atomic distances, pass through these solids, they can be diffracted due to the periodic structure of the crystal.

**Hint:** Think about how the regular arrangement of atoms in a crystal interacts with waves of similar size.

### Step 2: Understand the Reason
The reason states that "Interatomic distance in crystalline solids is of the order of 0.1 nm." This is also true. The interatomic distances in crystals are typically in the range of 0.1 nm (or 1 Ångström), which is comparable to the wavelength of X-rays. This similarity in scale is what allows the diffraction of X-rays to occur.

**Hint:** Consider the relationship between the size of the atoms and the wavelength of the X-rays used in the diffraction process.

### Step 3: Evaluate the Relationship Between Assertion and Reason
Since both the assertion and the reason are true, we need to determine if the reason correctly explains the assertion. The reason does explain why crystalline solids can cause X-rays to diffract, as the interatomic distance being on the order of the wavelength of X-rays is crucial for the diffraction phenomenon.

**Hint:** Reflect on whether the reason provides a valid explanation for the assertion.

### Conclusion
Both the assertion and the reason are true, and the reason correctly explains the assertion. Therefore, the correct answer is that both the assertion and the reason are true, and the reason is a correct explanation of the assertion.

**Final Answer:** Both the assertion and the reason are true, and the reason correctly explains the assertion.