Which of the following is correct match -

Down's syndrome is caused by trisomy of chromosome 21 (an extra copy of the 21st chromosome); correctly matched.
Sickle cell anaemia is an autosomal recessive disorder (gene on chromosome 11), not X-linked.
Haemophilia is X-linked recessive, not Y-linked.
Parkinson's disease is a neurodegenerative disorder, not caused by the X and Y chromosomes.
So the correct match is Down syndrome = 21st chromosome.