Question

Given below are two statements: Assertion (A): S. Typhi reduces sulphite to sulphide, to give a black metallic sheen on the colony in indicator media. Reason (R): Potassium Tellurite in Mc Leod's medium is reduced to metallic tellurium by Corynebacterium diphtheriae to produce black colony.

• A. Both (A) and (R) are correct and (R) is the correct explanation of (A)
• B. Both (A) and (R) are correct but (R) is not the correct explanation of (A)
• C. (A) is correct but (R) is not correct
• D. (A) is not correct but (R) is correct

Hint:

In assertion-reason questions, both statements may be true, but always check whether the reason actually explains the assertion.

Answer 1

The Correct Option is B

Concept:
In microbiology, selective and differential media are used to identify microorganisms based on their biochemical properties.

Step 1: Check Assertion (A).
Salmonella Typhi can reduce sulphite to sulphide. This reaction may produce black colonies or black metallic sheen in suitable indicator media. \[ A \text{ is correct} \]

Step 2: Check Reason (R).
Corynebacterium diphtheriae can reduce potassium tellurite to metallic tellurium in McLeod's medium, producing black colonies. \[ R \text{ is correct} \]

Step 3: Check whether R explains A.
Although both statements are correct, they describe two different organisms and two different biochemical reactions. Assertion is about S. Typhi, while Reason is about Corynebacterium diphtheriae. Therefore, Reason does not explain Assertion. \[ \therefore \text{Correct Answer is (B)} \]