The answer is (C) 75 Because ,
In (A)=LCM/HCF =180/45 = 4 , 4∈ N.
In (B)=LCM/HCF =180/60 = 3 , 3∈ N.
In (C)=LCM/HCF =180/75 = 2.4 , 2.4∉ N.
In (D)=LCM/HCF =180/90 = 2 , 2∈N.
Thus we see
in every case the HCF of the numbers divide the LCM completely except in (C).Since we know that HCF of a number should divide the LCM completely, the answer is