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 problem, we need to analyze the assertion and reason provided regarding the equivalent mass of potassium dichromate (K₂Cr₂O₇) when it acts as an oxidizing agent in acidic medium.

### Step 1: Understanding Equivalent Mass
The equivalent mass of a substance is calculated using the formula:
\[ \text{Equivalent mass} = \frac{\text{Molecular mass}}{n} \]
where \( n \) is the number of electrons gained or lost in the reaction.

### Step 2: Determine the Molecular Mass of K₂Cr₂O₇
The molecular mass of potassium dichromate (K₂Cr₂O₇) can be calculated as follows:
- Potassium (K) = 39.1 g/mol (2 K = 78.2 g/mol)
- Chromium (Cr) = 52.0 g/mol (2 Cr = 104.0 g/mol)
- Oxygen (O) = 16.0 g/mol (7 O = 112.0 g/mol)

So, the total molecular mass (M) of K₂Cr₂O₇ is:
\[ M = 78.2 + 104.0 + 112.0 = 294.2 \text{ g/mol} \]

### Step 3: Identify the Change in Oxidation State
In acidic medium, potassium dichromate (K₂Cr₂O₇) gets reduced. The oxidation state of chromium changes from +6 to +3. This indicates that each chromium atom gains 3 electrons during the reduction process.

### Step 4: Calculate the Total Electrons Transferred
Since there are 2 chromium atoms in K₂Cr₂O₇:
\[ \text{Total electrons gained} = 2 \times 3 = 6 \text{ electrons} \]

### Step 5: Calculate the Equivalent Mass
Now, substituting the values into the equivalent mass formula:
\[ \text{Equivalent mass} = \frac{M}{n} = \frac{294.2}{6} \approx 49.03 \text{ g/equiv} \]
This confirms that the equivalent mass of K₂Cr₂O₇ when it acts as an oxidizing agent in acidic medium is indeed \( \frac{M}{6} \).

### Step 6: Verify the Reason
The reason states that during reduction, the oxidation number of chromium changes from +6 to +3. This is correct as we have established that the chromium is reduced by gaining electrons.

### Conclusion
Both the assertion and the reason are correct. The assertion correctly states the equivalent mass as \( \frac{M}{6} \), and the reason correctly explains the change in oxidation state during the reduction process.

### Final Answer
Both the assertion and reason are true, and the reason is a correct explanation for the assertion.

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