What genetic condition is associated with trisomy 21 and results in intellectual disability?

Down's Syndrome is the correct answer as it is directly associated with trisomy 21, which occurs when an individual has three copies of chromosome 21 instead of the usual two. This additional genetic material disrupts normal development and is responsible for the characteristic features and developmental challenges faced by individuals with this condition, including intellectual disability. The condition encompasses a range of physical features and can also include other health complications.

The other options do not directly relate to trisomy 21. Intellectual disability is a broader term that can encompass various genetic and environmental conditions, but it does not specifically identify the condition associated with trisomy 21. Isomorphism is a concept mainly used in mathematics and biology and does not pertain to genetic conditions. Optimal complexity theory is a theoretical framework in the realm of complex systems, which also does not connect to genetic conditions. Therefore, Down's Syndrome is the most accurate and specific choice related to the question asked.