By what percentage does water expand when frozen?

Water expands approximately 9% when it freezes, which is closest to the percentage represented by the choice of 10%. This expansion occurs because the molecules of water form a crystalline structure when they transition from liquid to solid, resulting in a greater volume compared to the liquid state.

Understanding this property is important in various applications, such as in construction, where water might freeze in cracks or seams, leading to structural damage as the expanding ice exerts pressure. This knowledge is also crucial for outdoor activities, including those relevant to mountain warfare, where knowledge of environmental conditions can have significant operational implications.

Thus, while the other options may reflect different numbers, the choice that aligns most accurately with scientific data is indeed the one that signifies a 10% expansion, emphasizing the unique behavior of water as it freezes.