The correct option is A 10, 100
10, 100
100 is a multiple of 10, therefore 10 is the HCF of the pair.
100, 1000
1000 is a multiple of 100, therefore 100 is the HCF of the pair.
1000, 10000
10000 is a multiple of 1000, therefore 1000 is the HCF of the pair.
1, 100
100 is a multiple of 1, therefore 1 is the HCF of the pair.