It is given that the LCM of two numbers is 1200.
We know that the HCF of two numbers is always the factor of LCM
Checking all the options:
(a) 600 is the factor of 1200.
So this can be the HCF.
(b) 500 is not the factor of 1200.
So this cannot be the HCF.
(c) 400 is the factor of 1200.
So this can be the HCF.
(d) 200 is the factor of 1200.
So this can be the HCF.
Hence the correct choice is (b).