**Core Concept**
Acid-etching is a dental procedure that involves applying a mild acid to the surface of a tooth to create micro-retentions, which helps in the adhesion of dental restorative materials. This process is crucial in the preparation of the tooth for various dental procedures, such as bonding, veneers, and crowns.

**Why the Correct Answer is Right**
The correct answer is related to the preparation of the tooth surface for dental procedures. Acid-etching involves the application of a mild acid, usually phosphoric acid, to the tooth surface. This acid dissolves the smear layer and opens up the dentinal tubules, creating micro-retentions that allow for the adhesion of dental restorative materials. The enamel and dentin are etched, creating a surface that is receptive to bonding agents.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because acid-etching is not primarily used for the removal of plaque or calculus. While acid-etching may have some antibacterial effects, its primary purpose is to create a surface for bonding.

**Option B:** This option is incorrect because acid-etching is not a procedure used for the removal of decayed tooth structure. While acid-etching may be used in conjunction with other procedures for the removal of decay, it is not a standalone procedure for this purpose.

**Option C:** This option is incorrect because acid-etching is not a procedure used for the whitening of teeth. While acid-etching may have some effects on the surface of the tooth, it is not used for tooth whitening.

**Clinical Pearl / High-Yield Fact**
One important thing to remember is that acid-etching should be done for the correct duration to avoid over-etching, which can lead to damage to the tooth structure. The recommended duration for acid-etching is typically 15-30 seconds.

**Correct Answer:** D.