Here's why:

* Freezing: When you remove heat from a liquid, its molecules slow down and lose energy. This causes them to become more tightly packed, eventually forming a solid structure. This process is called freezing.

Let's look at the other options:

* 2. Solid to Liquid: This is the opposite process, called melting, and requires adding heat.

* 3. Gas: Removing heat from a gas can cause it to condense into a liquid (like water vapor turning into rain).

* 4. Gas: Removing heat from a gas can also cause it to solidify (like CO2 gas turning into dry ice).

In summary: Removing heat causes a substance to transition from a less ordered state (liquid or gas) to a more ordered state (solid).