## **Core Concept**
The question tests knowledge of dental materials, specifically gypsum products, which are widely used in dentistry for making dental casts, dies, and models. Gypsum products set through a chemical reaction that can be modified by adding accelerators or retarders to control the setting time.

## **Why the Correct Answer is Right**
Potassium sulfate is commonly used as an accelerator in gypsum products. It works by increasing the solubility of the gypsum particles, thereby speeding up the chemical reaction that leads to the setting of the gypsum. This is crucial in dental procedures where controlling the setting time can affect the accuracy and quality of the dental models or casts produced.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Sodium chloride (common salt) can affect the setting of gypsum but is not the most commonly used accelerator.
- **Option B:** Sodium carbonate can influence the properties of gypsum products but is not typically used as an accelerator.
- **Option D:** Aluminum sulfate can act as a retarder or affect the properties of gypsum but is not the most common accelerator added.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the addition of accelerators or retarders to gypsum products can significantly affect their working and setting times. Potassium sulfate is specifically noted for its effectiveness as an accelerator, making it a valuable additive in clinical and laboratory settings where gypsum products are used.

## **Correct Answer:** . Potassium sulfate.