Final answer:
A person with Down syndrome has trisomy of chromosome 21, resulting in 47 chromosomes in their somatic cells. The correct answer is option B) 47 chromosomes; 23 autosomes.
Step-by-step explanation:
A person with Down syndrome has trisomy of chromosome 21, which means they have an extra copy of chromosome 21. Therefore, the correct answer is option B) 47 chromosomes; 23 autosomes. In a somatic cell of a person with Down syndrome, there are 47 chromosomes instead of the usual 46.