A: Equivalent mass of `K_(2) Cr_(2),O_(7)`, when it acts as an oxidizing agent in acidic medium is M//6.
R: During reduction, oxidation number of chromium changes from +6 to +3.

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 equivalent mass of potassium dichromate (K₂Cr₂O₇) when it acts as an oxidizing agent in acidic medium, we will follow these steps:

### Step 1: Understand the Assertion
The assertion states that the equivalent mass of K₂Cr₂O₇ when it acts as an oxidizing agent in acidic medium is M/6.

### Step 2: Determine the Reaction
In acidic medium, potassium dichromate (K₂Cr₂O₇) acts as a strong oxidizing agent. The balanced chemical reaction when K₂Cr₂O₇ reacts with sulfuric acid (H₂SO₄) can be represented as:
\[ K_2Cr_2O_7 + 4H_2SO_4 \rightarrow K_2SO_4 + 2Cr_2(SO_4)_3 + 4H_2O + 3O_2 \]

### Step 3: Analyze the Change in Oxidation State
In this reaction, the oxidation state of chromium changes from +6 in K₂Cr₂O₇ to +3 in Cr₂(SO₄)₃.

### Step 4: Calculate the Change in Oxidation Number
For each chromium atom, the change in oxidation state is:
\[ +6 \text{ (in K₂Cr₂O₇)} \rightarrow +3 \text{ (in Cr₂(SO₄)₃)} \]
The change per chromium atom is:
\[ 6 - 3 = 3 \]
Since there are 2 chromium atoms in K₂Cr₂O₇, the total change in oxidation state for the molecule is:
\[ 2 \times 3 = 6 \]

### Step 5: Calculate the Equivalent Mass
The equivalent mass (or equivalent weight) of a substance is calculated using the formula:
\[ \text{Equivalent mass} = \frac{\text{Molecular mass}}{\text{x factor}} \]
Here, the x factor is the total change in oxidation number, which we calculated as 6. Thus, the equivalent mass of K₂Cr₂O₇ is:
\[ \text{Equivalent mass} = \frac{M}{6} \]
where M is the molecular mass of K₂Cr₂O₇.

### Conclusion
Both the assertion and the reason provided are correct. The assertion states the equivalent mass of K₂Cr₂O₇ is M/6, and the reason explains that the oxidation number of chromium changes from +6 to +3 during the reduction process.