 Hi, and welcome to the session. I am Shashi and I am going to help you to solve the following question. Question is, in star, defined on the set 1,2,3,4,5 by A star B is equal to LCM of A and B, our binary operation, justify our answer. Let us start with the solution now. The set 1,2,3,4,5 is defined by A star B equal to LCM of A and B. Now, if we take two elements of the set, that is 4 and 5 and 5, 4 star 5, which is equal to LCM of 4 and 5, LCM of 4 and 5 is equal to 20. So, we get 4 star 5 is equal to 20, but 20 does not belongs to the given set. Since all LCMs do not belong to the set 1,2,3,4,5, so star is not a binary operation. So, our final answer is no, star is not a binary operation. Right? This completes the session. Hope you understood the session. Take care and goodbye.