## **Core Concept**
The question tests the identification of a gram-negative coccus that grows on chocolate agar, a type of enriched medium used for cultivating fastidious organisms. Chocolate agar supports the growth of various bacteria, including *Neisseria* species, which are gram-negative cocci.

## **Why the Correct Answer is Right**
The correct answer, *Neisseria gonorrhoeae*, is a gram-negative coccus that causes gonorrhea, a sexually transmitted infection. This organism is known for its requirement of specific nutrients, such as X (hemin) and V (nicotinamide adenine dinucleotide, NAD) factors, which are provided by chocolate agar. *N. gonorrhoeae* appears as gram-negative cocci, often described as coffee bean-shaped diplococci.

## **Why Each Wrong Option is Incorrect**
* **Option A:** *Streptococcus pneumoniae* is a gram-positive coccus, not gram-negative, and does not match the description.
* **Option B:** *Moraxella catarrhalis* is a gram-negative coccobacillus rather than a coccus and, while it can grow on chocolate agar, it's less commonly associated with pus cultures in this context.
* **Option D:** *Escherichia coli* is a gram-negative rod, not a coccus, and grows on a variety of agar types, not specifically requiring chocolate agar.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that *Neisseria gonorrhoeae* requires chocolate agar for growth due to its need for X and V factors. This is a critical clue in identifying the organism in clinical microbiology.

## **Correct Answer:** .