The correct answer is Pyrophosphates or zinc citrate.

- Dental calculus, also known as tartar, is formed by the mineralization of dental plaque.
- To control its formation, certain ingredients are added to dentifrices (toothpastes and powders).
- Pyrophosphates and zinc citrate are commonly included because they act as chelating agents that inhibit the crystallization and deposition of calcium phosphate salts on the tooth surface, thereby preventing the formation of dental calculus.

Other options:
- Fluoride compounds are primarily included to enhance enamel remineralization and prevent dental caries but do not specifically inhibit calculus formation.
- Triclosan is an antimicrobial agent aimed at controlling plaque and gingivitis but has limited or no direct effect on calculus inhibition.
- Potassium nitrate is used as a desensitizing agent to reduce dentinal hypersensitivity, not for calculus control.

Therefore, dentifrices formulated to reduce calculus often contain pyrophosphates or zinc citrate as active ingredients targeting the mineralization process.

Reference: Textbook of Oral Physiology, Volume 2, Chapter 5, Page 134