A: `Cr_(2)O_(7)^(-2)`, 2 is orange in colour
R: It is due to the presence of unpaired electrons in d-subshell of Cr.

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 and reason provided, we will break down the information step by step.

### Step 1: Analyze the Assertion
The assertion states that \( \text{Cr}_2\text{O}_7^{2-} \) is orange in color. This is a known fact in chemistry. The color of transition metal compounds often arises from d-d transitions or charge transfer processes.

**Hint:** Consider the common colors associated with different oxidation states of chromium compounds.

### Step 2: Determine the Oxidation State of Chromium
To understand why \( \text{Cr}_2\text{O}_7^{2-} \) is orange, we need to calculate the oxidation state of chromium in this compound.

The formula for the oxidation state can be set up as follows:
- Let the oxidation state of chromium be \( x \).
- The oxidation state of oxygen is -2.
- The compound has 2 chromium atoms and 7 oxygen atoms.

Setting up the equation:
\[ 2x + 7(-2) = -2 \]
\[ 2x - 14 = -2 \]
\[ 2x = 12 \quad \Rightarrow \quad x = +6 \]

**Hint:** Remember to account for the total charge of the compound when calculating oxidation states.

### Step 3: Write the Electron Configuration of Chromium
The electron configuration of chromium (Cr) in its elemental state is:
\[ \text{Cr}: [\text{Ar}] 3d^5 4s^1 \]

When chromium is in the +6 oxidation state, it loses 6 electrons:
\[ \text{Cr}^{+6}: [\text{Ar}] 3d^0 4s^0 \]

This means that there are no electrons in the d-subshell of chromium in the +6 oxidation state.

**Hint:** Pay attention to how oxidation states affect electron configurations.

### Step 4: Analyze the Reason
The reason states that the orange color is due to the presence of unpaired electrons in the d-subshell of chromium. However, since \( \text{Cr}^{+6} \) has no electrons in the d-subshell (3d^0), there are no unpaired electrons.

**Hint:** Consider how the presence or absence of unpaired electrons affects the color of transition metal complexes.

### Step 5: Conclusion
Based on the analysis:
- The assertion that \( \text{Cr}_2\text{O}_7^{2-} \) is orange is true.
- The reason that it is due to unpaired electrons in the d-subshell is false.

Thus, the correct answer is that the assertion is true, but the reason is false.

**Final Answer:** Assertion (A) is true, Reason (R) is false.