NCERT Example 11 - Sets
Question: If A belongs to B and B is a subset of C, is A necessarily a subset of C?
Answer: No. For A = {1}, B = {{1}, 2}, C = {{1}, 2, 3}, A belongs to B and B subset C, but A is not a subset of C.
Full step-by-step NCERT solution with diagrams on Something by Zero.