**Core Concept**
The placement of indirect retainers in removable partial dentures (R.P.D) is crucial for the stability and retention of the prosthesis. Indirect retainers act as a mechanical lock to prevent the denture from tilting or rotating, thereby enhancing the overall stability and patient satisfaction.

**Why the Correct Answer is Right**
The indirect retainer is placed on the edentulous side of the remaining natural teeth, typically on the mesial surface of the abutment tooth. This placement allows the indirect retainer to engage with the occlusal surface of the opposing tooth, thereby creating a mechanical lock that prevents the denture from tilting or rotating. The placement of indirect retainers also helps to distribute the forces of mastication more evenly, reducing the stress on the abutment teeth and the surrounding tissues.

**Why Each Wrong Option is Incorrect**
* **Option A:** Incorrect because indirect retainers are not typically placed on the lingual surface of the abutment tooth. The lingual surface is often used for other components of the R.P.D, such as clasps or attachments.
* **Option B:** Incorrect because indirect retainers are not typically placed on the buccal surface of the abutment tooth. The buccal surface is often used for other components of the R.P.D, such as clasps or attachments, and is not ideal for indirect retainers due to the risk of tooth wear and irritation to the buccal mucosa.
* **Option C:** Incorrect because indirect retainers are not typically placed on the distal surface of the abutment tooth. The distal surface is often used for other components of the R.P.D, such as clasps or attachments, and is not ideal for indirect retainers due to the risk of tooth wear and irritation to the lingual mucosa.

**Clinical Pearl / High-Yield Fact**
When designing an indirect retainer, it is essential to consider the occlusal scheme and the forces of mastication to ensure that the retainer engages with the opposing tooth in a way that prevents tilting or rotation of the denture. A well-designed indirect retainer can significantly enhance the stability and retention of the R.P.D.

**Correct Answer: D.**