The correct answer is option 2, plaster of Paris. Plaster of Paris is a white material that is commonly used in medical applications for immobilizing fractured bones. When mixed with water, it forms a paste-like consistency that can be molded and applied to the affected area.

Option 1, bleaching powder, is not the correct answer because it is not commonly used in medical procedures for bone fractures. Bleaching powder, or calcium hypochlorite, is primarily used as a cleaning agent and disinfectant.

Option 3, powder of zinc oxide, is also not the correct answer. While zinc oxide is commonly used in various medical applications, such as sunscreen and wound healing, it is not typically used for fixing fractured bones.

Option 4, lime powder, is also incorrect as it is not commonly used for immobilizing fractured bones. Lime powder, or calcium hydroxide, is often used in construction applications like mortar and plaster, but not for medical purposes.

Thus, option 2, plaster of Paris, is the correct answer as it is the commonly used white material that forms a paste when mixed with water and is used to maintain fractured bones in place.