## Core Concept
The question pertains to the nomenclature of chromosome arms based on their lengths. Chromosomes are composed of two arms, a long arm and a short arm, which are separated by a centromere. The designations of these arms are crucial in cytogenetics for identifying specific chromosomal abnormalities.

## Why the Correct Answer is Right
The long arm of a chromosome is designated as **q**, and the short arm is designated as **p**. This nomenclature is universally accepted in genetics and is critical for describing chromosomal abnormalities. The terms "long" and "short" refer to the relative lengths of the arms, which can vary slightly among different chromosomes but are consistently labeled as p for the short arm and q for the long arm.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because it reverses the standard nomenclature; the short arm is not designated as "q" and the long arm as "p".
- **Option B:** This option is incorrect for the same reason as Option A; it also misrepresents the standard nomenclature.
- **Option D:** This option is incorrect because it suggests an alternative nomenclature that is not standard in cytogenetics.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the "p" arm is typically the short arm, and the "q" arm is the long arm of a chromosome. This nomenclature is essential for understanding and communicating about chromosomal abnormalities, such as translocations, deletions, and duplications.

## Correct Answer Line
**Correct Answer: C. p and q.**