**Core Concept**
The cell wall of Gram-positive bacteria is a critical component that provides structural support and maintains the integrity of the bacterial cell. It is composed of a thick peptidoglycan layer (also known as murein) that is cross-linked by short peptides, which confers rigidity and resistance to osmotic pressure.

**Why the Correct Answer is Right**
The correct answer is related to the composition of the Gram-positive cell wall. Gram-positive bacteria have a thick peptidoglycan layer, but they also have a unique feature: the presence of teichoic acids, which are covalently linked to the peptidoglycan layer. Teichoic acids play a crucial role in maintaining the integrity of the cell wall and are involved in the regulation of cell growth and division.

**Why Each Wrong Option is Incorrect**
**Option A:** This statement is true about the Gram-positive cell wall. The peptidoglycan layer is indeed the main component of the cell wall, providing structural support and maintaining osmotic balance.
**Option B:** This statement is also true. The presence of teichoic acids in Gram-positive bacteria is a characteristic feature of their cell walls, and they play a crucial role in maintaining cell wall integrity.
**Option C:** This statement is incorrect. Gram-positive bacteria do not have a mycolic acid layer in their cell walls. Mycolic acids are a type of lipid found in the cell walls of Mycobacterium species, such as M. tuberculosis.

**Clinical Pearl / High-Yield Fact**
The Gram stain test is a widely used technique for differentiating between Gram-positive and Gram-negative bacteria. The test relies on the ability of the bacterial cell wall to retain or lose a crystal violet dye in the presence of an alcohol-based decolorizer. Gram-positive bacteria retain the dye and appear purple under a microscope, while Gram-negative bacteria lose the dye and appear pink.

**Correct Answer: C.**