How will be the flow of heat if iron ball at 40degree celsius is dropped in mug containing water at40 degree celsius?

Heat will flow from the iron ball to the water in the mug until they reach thermal equilibrium, meaning both the iron ball and the water will eventually reach the same temperature. This process is governed by the laws of thermodynamics, specifically the second law which states that heat will always transfer from a hotter object to a cooler object until they reach the same temperature.