Which of the following is a chromosomal disorder?

The correct answer is Option (4) → Down's syndrome

Option (4) Down's syndrome — Correct. Chromosomal disorders are caused by the absence, excess or abnormal arrangement of chromosomes. Down’s syndrome is caused by an extra copy of chromosome 21 (trisomy 21), so it is a chromosomal disorder.

Note: A similar question was also asked in CUET (UG) 2026 on 30-05-2026 (Slot 2).

NCERT Extract:
Mendelian Disorders – “Broadly, genetic disorders may be grouped into two categories – Mendelian disorders and Chromosomal disorders. Mendelian disorders are mainly determined by alteration or mutation in the single gene. These disorders are transmitted to the offspring on the same lines as we have studied in the principle of inheritance. The pattern of inheritance of such Mendelian disorders can be traced in a family by the pedigree analysis. Most common and prevalent Mendelian disorders are Haemophilia, Cystic fibrosis, Sickle-cell anaemia, Colour blindness, Phenylketonuria, Thalassemia, etc.”
Chromosomal Disorders – “… Down’s syndrome, Turner’s syndrome, Klinefelter’s syndrome are common examples of chromosomal disorders.”