Explanation:

- Down Syndrome (Option 3): This is the correct term for Trisomy 21. It's a genetic disorder caused by the presence of an extra chromosome 21. It results in developmental and physical changes, including cognitive impairment and distinct facial features.

- Evans Syndrome (Option 1): This is an autoimmune disorder where the body attacks its own red blood cells and platelets, not related to chromosome abnormalities.

- Edwards Syndrome (Option 2): Also known as Trisomy 18, it's another chromosomal disorder, but it involves an extra chromosome 18. It is distinct from Down Syndrome.

- Gray Baby Syndrome (Option 4): This is not a chromosomal disorder. It's an adverse effect from an antibiotic called chloramphenicol in newborns, causing symptoms like a gray skin tone.