To determine the correct answer, let's analyze the behavior of [tex]$H_2O$[/tex] molecules in comparison to most other molecules when they are cooled.
1. Behavior of Most Molecules:
- For most molecules, when the temperature is reduced (i.e., when they are cooled), they contract. This means the molecules come closer together, and the volume decreases.
- This contraction happens consistently as they are cooled to lower and lower temperatures until they reach a solid state.
2. Behavior of [tex]$H_2O$[/tex] Molecules:
- Water behaves differently compared to most substances. While water does contract when cooled initially, it starts to behave differently as it approaches [tex]$0^{\circ}C$[/tex].
- From [tex]$4^{\circ}C$[/tex] down to [tex]$0^{\circ}C$[/tex], water expands instead of contracting. This is due to the unique structure of ice crystals that form when water freezes, which occupy more space than in the liquid state.
Based on the provided analysis, let's evaluate each option:
- Option A: "They contract when cooled to [tex]$4^{\circ}C$[/tex]."
- This option is not correct because [tex]$H_2O$[/tex] does not contract when cooled to [tex]$4^{\circ}C$[/tex]. In fact, water is at its densest point at [tex]$4^{\circ}C$[/tex], and cooling it further results in expansion, not contraction.
- Option B: "They contract when cooled to [tex]$0^{\circ}C$[/tex]."
- This option correctly describes the behavior of most molecules. Most substances contract as they are cooled down to [tex]$0^{\circ}C$[/tex].
- However, it does not describe the behavior of [tex]$H_2O$[/tex] molecules, which expand when cooled to [tex]$0^{\circ}C$[/tex].
- Option C: "They expand when cooled to [tex]$4^{\circ}C$[/tex]."
- This option is not accurate either. [tex]$H_2O$[/tex] molecules do not expand at [tex]$4^{\circ}C$[/tex]. Expansion occurs as water cools further below [tex]$4^{\circ}C$[/tex].
Therefore, the correct answer is:
- Option B: "They contract when cooled to [tex]$0^{\circ}C$[/tex]."
Hence, the behavior of most molecules contracting when cooled to [tex]$0^{\circ}C$[/tex] matches the general trend seen in most substances.
