<prompt> Most common chromosomal syndrome is:Fragile X-syndromeTrisomy 17Trisomy 21Trisomy 13  <response>: c. Trisomy 21Ref: Nelsons 20e p 618-619Down syndrome Trisomy 21 is the most common of the chromosomal disorder.Trisomy 16 is the most common trisomy overall, however most do not survive and die in utero Hence, among the live births, or among children, most common chromosomal abnormality is Trisomy 21 