A child come with fever, cold, cough, membrane over tonsils; nasal swab is taken, culture should be done on which medium for earliest diagnosis –

**Core Concept**
The underlying principle being tested is the identification of a specific bacterial pathogen, *Corynebacterium diphtheriae*, which causes diphtheria, characterized by a membrane over the tonsils. The diagnosis of diphtheria requires the isolation of the bacteria.

**Why the Correct Answer is Right**
The correct medium for the isolation of *Corynebacterium diphtheriae* is **Tellurite agar** or **Hoyle's tellurite agar**, as tellurite inhibits the growth of other bacteria while allowing *C. diphtheriae* to grow.

**Why Each Wrong Option is Incorrect**
**Option A:** Inappropriate for *C. diphtheriae*.
**Option B:** Not specific for diphtheria.
**Option D:** Used for other types of bacteria.

**Clinical Pearl / High-Yield Fact**
Diphtheria diagnosis relies on clinical presentation and laboratory confirmation, with **Tellurite agar** being key for bacterial isolation.

**Correct Answer:** D. Tellurite agar.

✓ Correct Answer: A. Loffler's serum slop