On a particular day A and B decide that they would either speak the truth or will lie. C asks A whether he is speaking truth or lying? He answers and B listens to what he said. C then asks B what A has said B says "A says that he is a liar" What is B speaking?

If A says 'I am a liar', this creates a logical paradox. If A is truthful, he cannot truthfully say he's a liar. If A is lying, then the statement 'I am a liar' is false, meaning he's truthful - contradiction. Therefore A cannot consistently make this statement. B claims 'A says that he is a liar' - since A cannot consistently say this, B must be lying.