ANS:C - Malleable iron

Among the options provided, malleable iron is most likely to resist maximum shock and vibration without cracking. Malleable iron is a type of cast iron that has been heat-treated to convert the brittle iron carbide (Fe3C) in the microstructure into a ductile and resilient form of carbon. This heat treatment process, known as annealing or malleablizing, imparts improved toughness and ductility to the material, making it less prone to cracking under shock and vibration compared to other types of cast iron. Grey cast iron and white cast iron are both brittle forms of cast iron and are more susceptible to cracking under shock and vibration. Grey cast iron contains graphite flakes in its microstructure, which act as stress concentration points and make it relatively brittle. White cast iron contains cementite (iron carbide) in its microstructure, making it even more brittle than grey cast iron. Graphite, on its own, is not a type of cast iron but rather a form of carbon. While graphite is relatively soft and can deform under stress, it does not possess the mechanical properties necessary to resist shock and vibration to the same extent as malleable iron. Therefore, malleable iron is the most suitable option for resisting maximum shock and vibration without cracking.