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 ?

B is speaking a lie. If A were telling the truth and said 'I speak truth', B would report this truthfully. But B says 'A says that he is a liar', which contradicts what A would actually say. If A were lying and said 'I am a liar', this would be a true statement about lying, creating a paradox - a liar cannot truthfully claim to be a liar. The only consistent scenario is that A truthfully said 'I speak truth', and B lied about what A said. This classic logic puzzle tests understanding of truth-teller/liar paradoxes.