Answer: Tony has explicitly breached the Implied Warranty of Fitness for a particular purpose.
Explanation: the Implied warranty of fitness for a particular purpose takes effect when a buyer specifically asks a seller for a product that can be used for a particular purpose.
Because Mark (buyer) requested for the exact type of wood that can resist wood decay caused due to the damp environment of his cabin and Tony (seller) sells Mark lumber while assuring him that it's what he is looking for. Tony's assurance to Mark is known as the Implied warranty of fitness for a particular purpose, and since the wood is affected by dampness and caves then Tony has explicitly breached the warranty.
