Does mercury expand when it is frozen?

Mercury behaves differently than most substances when it comes to freezing. When mercury freezes, it does not expand; instead, it contracts. This is in contrast to water, which expands when it freezes due to the formation of a crystalline structure in ice. Mercury's unique molecular arrangement causes it to occupy less volume when solidified, leading to a decrease in volume rather than an increase.

Understanding this property is essential, especially in contexts like thermometers, where mercury's behavior allows for accurate temperature readings across a range of conditions. The other options suggest scenarios that either imply that mercury behaves like water or conditionally expands, which is not supported by its physical properties. Thus, the correct response reflects mercury's contraction upon freezing.