**Core Concept**
Dental stone and dental plaster are both used in dental casting, but they differ primarily in their particle characteristics. While both are mixtures of calcium sulfate and water, the key distinction lies in the physical form of their particles, which affects mixing, setting time, and final casting properties.

**Why the Correct Answer is Right**
Dental stone is made from a fine, uniform particle size and spherical shape, which ensures smooth, accurate casts with minimal shrinkage. Dental plaster, in contrast, uses coarser, irregularly shaped particles that result in a more porous and less precise cast. These differences in **shape and size of particles** directly influence the surface finish, dimensional accuracy, and flow during mixing. The particle morphology affects the rate of hydration and the final density of the cast.

**Why Each Wrong Option is Incorrect**
Option A: Chemical composition is nearly identical in both materials—both are based on calcium sulfate hemihydrate (gypsum). Thus, this is not the main difference.
Option B: Self-life (setting time) differs slightly, but this is a secondary factor and not the primary distinction.
Option D: Solubility in water is similar for both materials; neither is highly soluble, so water solubility is not the key differentiator.

**Clinical Pearl / High-Yield Fact**
Always remember: **"Dental stone gives better accuracy due to finer, spherical particles"**—this is why it’s preferred for precise dental models and crowns.

✓ Correct Answer: C. Shape and size of particles