Question

Assertion (A) : Highest oxidation state of Mn is +7 in first series of transition elements. Reason (R) : Transition metals exhibit variable oxidation states.

• A. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
• B. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
• C. Assertion (A) is true, but Reason (R) is false.
• D. Assertion (A) is false, but Reason (R) is true.

Hint:

Manganese has the electronic configuration \[ [Ar]\,3d^5\,4s^2 \] and can utilize all seven valence electrons, giving the maximum oxidation state of \[ +7. \] This is why compounds such as \(KMnO_4\) contain manganese in the \(+7\) oxidation state.

Answer 1

The Correct Option is B

Step 1: Find all valence electrons available in Mn.
Manganese (Z = 25) has configuration $[Ar]\,3d^5\,4s^2$, giving 7 valence electrons. Under suitable conditions all 7 can be used in bonding, so Mn can reach an oxidation state of $+7$ (as in $KMnO_4$). No other first-series transition element routinely exceeds $+7$. The Assertion is true.
Step 2: Verify the Reason independently.
Transition metals exhibit variable oxidation states because both $(n-1)d$ and $ns$ electrons can participate in bonding. This general statement is correct, so the Reason is true.
Step 3: Check whether the Reason explains the Assertion.
The Assertion asks specifically why Mn reaches $+7$ as the highest value. The actual explanation is that Mn has $3d^5\,4s^2$ providing 7 valence electrons, all available for bonding. The Reason only states the general property of variable oxidation states; it does not explain why Mn specifically reaches $+7$. Therefore the Reason is true but is not the correct explanation of the Assertion.
\[ \boxed{\text{Option (B)}} \]