The opacity in ceramics is achieved by adding:
**Core Concept**
Ceramics exhibit opacity due to the presence of certain materials that interact with visible light. The opacity in ceramics is primarily achieved through the addition of a specific substance that absorbs or scatters light.
**Why the Correct Answer is Right**
The correct answer is **Zirconia**. Zirconia (ZrO2) is a common opacifier used in ceramic materials. When added to ceramic glazes, zirconia particles scatter light in all directions, creating an opaque effect. This is due to the large difference in refractive indices between the zirconia particles and the surrounding glass matrix, which causes light to be scattered and absorbed.
**Why Each Wrong Option is Incorrect**
* **Option A:** **Alumina** is often used as a refractory and strengthening agent in ceramics, but it does not typically contribute to opacity.
* **Option B:** **Silica** is a primary component of many ceramic materials, but it is not an opacifier.
* **Option C:** **Titania** is used in some ceramic applications, but it is not typically used as an opacifier.
**Clinical Pearl / High-Yield Fact**
In ceramics, the choice of opacifier can significantly impact the final product's appearance and durability. Understanding the properties of different materials is crucial for selecting the appropriate opacifier for a specific application.
**Correct Answer: D. Zirconia**