Here's why:
* Solids: Elements in their solid state are the most common. They have a fixed shape and volume.
* Liquids: There are far fewer elements that are liquid at room temperature (think mercury and bromine).
* Gases: Even fewer elements exist as gases at room temperature (think oxygen, nitrogen, hydrogen).
While the exact number varies depending on how you define "most," the majority of elements on the periodic table are indeed solids.