## Core Concept
The question tests knowledge of dental hygiene products, specifically tartar control toothpaste. Tartar, also known as dental calculus, is a hardened deposit that forms on teeth. The active ingredients in tartar control toothpaste aim to prevent the formation of tartar or reduce its accumulation.

## Why the Correct Answer is Right
The correct answer, **Pyrophosphates**, specifically sodium pyrophosphate, is an active ingredient in some tartar control toothpastes. Pyrophosphates work by inhibiting the formation of tartar (dental calculus) on teeth. They do this by blocking the attachment of calcium and phosphate ions, which are essential for tartar formation. This mechanism helps in preventing the accumulation of tartar, thereby aiding in the maintenance of good oral hygiene.

## Why Each Wrong Option is Incorrect
- **Option A:** While various chemicals can be used in toothpaste for different purposes, **Zinc chloride** is primarily known for its antibacterial properties and is not the primary active ingredient for tartar control.
- **Option B:** **Sodium fluoride** is commonly used in toothpaste for its role in preventing tooth decay (dental caries) by making teeth more resistant to acid attacks from plaque bacteria and sugars in the mouth. It is not primarily used for tartar control.
- **Option C:** This option is left blank, implying it could potentially be the correct answer based on the question format provided.

## Clinical Pearl / High-Yield Fact
A key point to remember is that **pyrophosphates**, such as sodium pyrophosphate, are used in tartar control toothpastes to prevent calculus formation. This is a high-yield fact for dental and pharmacology exams.

## Correct Answer Line
**Correct Answer: D. Pyrophosphates.**