Here's why:
* Water: This is the most common example. The reason for this unusual behavior lies in the structure of water molecules. In liquid water, the molecules are close together, but they can move around freely. In ice, the molecules form a rigid crystalline structure with empty spaces between them. This structure makes ice less dense than liquid water, which is why ice floats.
* Gallium: This is a soft, silvery metal with a very low melting point (around 29.76 °C). Similar to water, the solid structure of gallium has more empty space than the liquid structure.
It's important to note that most substances become denser in their solid state. This is because the molecules are packed closer together in a solid, making it more compact. However, the unique structure of water and gallium leads to them becoming less dense in their solid forms.
