**Core Concept**
Trisomy refers to a genetic disorder caused by the presence of an extra chromosome, resulting in an abnormal number of chromosomes in the cells of an individual. This condition can lead to various physical and developmental abnormalities.

**Why the Correct Answer is Right**
Down syndrome, also known as Trisomy 21, is the most common trisomy, occurring in approximately 1 in 700 births. It is caused by the presence of an extra copy of chromosome 21, leading to an abnormal number of genes being expressed. The extra genetic material disrupts normal cell division and development, resulting in characteristic physical features and intellectual disabilities.

**Why Each Wrong Option is Incorrect**
**Option A:** Edward syndrome (Trisomy 18) is a rare chromosomal disorder with a higher mortality rate than Down syndrome.
**Option B:** Patau syndrome (Trisomy 13) is another rare chromosomal disorder with severe intellectual disability and physical abnormalities.
**Option C:** Trisomy 16 is a common trisomy in miscarriages but not typically viable in live births.

**Clinical Pearl / High-Yield Fact**
Down syndrome is often associated with a characteristic facial appearance, including a flat face, small ears, and an upward slanting eye. It is essential to recognize these features to provide early diagnosis and management.

**Correct Answer: C. Trisomy 16.**