**Core Concept**
The phenomenon of moisture absorption by an alginate impression is related to the physical properties of alginate materials used in dentistry. Alginate impression materials are hydrocolloid-based and exhibit a unique ability to absorb and retain water, which affects their dimensional stability.

**Why the Correct Answer is Right**
The absorption of moisture by alginate impression materials is due to their hydrophilic nature, which allows them to interact with water molecules. This interaction leads to an increase in the material's volume and a subsequent change in its shape. The rate of absorption is influenced by factors such as the concentration of alginate, the temperature, and the presence of other substances that may affect the material's hydrophilicity.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the phenomenon of moisture absorption by alginate impression materials. The term "swelling" is often associated with the absorption of water by hydrocolloid materials, but it does not capture the full complexity of the process.

**Option B:** This option is incorrect because it is not a recognized term in the field of dentistry or materials science. While it may sound plausible, it is not a valid description of the phenomenon in question.

**Option C:** This option is incorrect because it refers to a different property of alginate impression materials. While they do exhibit a degree of elasticity, this is not directly related to their ability to absorb moisture.

**Option D:** This option is incorrect because it is not a recognized term in the field of dentistry or materials science. While it may sound plausible, it is not a valid description of the phenomenon in question.

**Clinical Pearl / High-Yield Fact**
It's essential to note that the dimensional stability of alginate impression materials can be affected by the presence of saliva, blood, or other substances that may alter their hydrophilic properties. This can lead to inaccuracies in dental impressions and restorations.

**Correct Answer: B. Sorption.**