**Core Concept**
Corynebacterium diphtheriae is a Gram-positive, pleomorphic bacterium that causes diphtheria. Tellurite agar is a selective medium used to isolate and differentiate C diphtheriae from other bacteria.

**Why the Correct Answer is Right**
C diphtheriae grows in Tellurite agar due to its resistance to tellurite ions. The bacterium reduces tellurite to metallic tellurium, which is visible as black colonies on the agar. This process takes around 1-2 days, allowing for the selective growth of C diphtheriae. The reduction of tellurite is mediated by the enzyme tellurite reductase, which is produced by C diphtheriae.

**Why Each Wrong Option is Incorrect**
* **Option A:** 2-4 hours is too short for C diphtheriae to grow in Tellurite agar, as the reduction of tellurite requires time and metabolic activity.
* **Option B:** 4-8 hours is still too short, and the colonies may not be visible due to the slow growth and reduction of tellurite.
* **Option C:** 8-12 hours is closer but still not accurate, as the growth and reduction of tellurite require a longer period.

**Clinical Pearl / High-Yield Fact**
C diphtheriae is a notifiable disease, and its isolation requires specialized media like Tellurite agar. The bacterium produces a potent toxin that can cause severe respiratory and cardiac complications.

**✓ Correct Answer: D. 1-2 days**