Read the following text and answer the following questions on the basis of the same: Down syndrome (sometimes called Down's syndrome) is a condition in which a child is born with an extra copy of their 21st chromosome hence its other name, trisomy 21. The affected individual mental retarded, short statured with small round, head, furrowed tongue and partially open mouth, Physical, psychomotor and mental development is retarded.
Down syndrome is

Options

A. Sex-linked
B. Chromosomal
C. dominant
D. recessive

Explanation

### Step-by-Step Solution:

1. **Understanding Down Syndrome**:
- Down syndrome is a genetic condition caused by the presence of an extra copy of the 21st chromosome, which is also referred to as trisomy 21.

2. **Identifying Characteristics**:
- Individuals with Down syndrome often exhibit specific physical characteristics such as a small round head, a furrowed tongue, and a partially open mouth. They also tend to have short stature and experience delays in physical, psychomotor, and mental development.

3. **Cause of Down Syndrome**:
- The condition arises due to a genetic anomaly known as non-disjunction, where the 21st chromosome fails to separate properly during gamete formation. This results in a gamete with two copies of the 21st chromosome.

4. **Formation of the Zygote**:
- When a gamete with an extra chromosome fuses with a normal gamete from another parent, the resulting zygote will have three copies of the 21st chromosome, leading to Down syndrome.

5. **Classifying Down Syndrome**:
- Based on the information provided, Down syndrome is classified as a chromosomal disorder due to the abnormal number of chromosomes present (specifically, an extra chromosome).

6. **Selecting the Correct Option**:
- The options provided were: Sex-linked, Chromosomal, Dominant, or Recessive. Given that Down syndrome is caused by a chromosomal abnormality, the correct answer is **Chromosomal**.

### Final Answer:
Down syndrome is a **Chromosomal** disorder.

---