The correct answer is Zinc oxide-eugenol.

- Among the given options, zinc oxide-eugenol is well-known for its bactericidal properties and is commonly used in periodontal dressings.
- The eugenol component gives the material its antimicrobial effect, helping to reduce bacterial contamination and promote healing after periodontal surgery or procedures.
- Additionally, zinc oxide-eugenol provides a soothing effect on the tissues and acts as a protective barrier.

- Other options such as aluminum chloride, ferric sulfate, and tannic acid are primarily used as hemostatic agents or astringents to control bleeding by protein precipitation and vascular constriction, but they do not possess significant bactericidal properties nor are they routinely used in periodontal dressings.

Key points:
- Zinc oxide-eugenol has bactericidal effects due to eugenol.
- It is frequently used in periodontal dressings to aid healing and protect surgical sites.
- Other astringents like aluminum chloride, ferric sulfate, and tannic acid primarily control bleeding but lack the antimicrobial action needed for dressings.

Reference: Harold Cohen, Richard S. Schwarz, "Oral Medicine and Diagnosis," Volume 1, Chapter 10, pp. 234-236