Here's a breakdown:

* Gas Giants: Jupiter and Saturn are primarily composed of hydrogen and helium, the lightest elements.

* Ice Giants: Uranus and Neptune have a smaller proportion of hydrogen and helium, but their compositions are dominated by heavier elements, such as oxygen, carbon, nitrogen, and sulfur, which are present in the form of ices at the extremely low temperatures of these planets.

It's important to note that even though the "ice" giants are mostly composed of ice, it's not like the solid ice we see on Earth. Instead, these ices are present as very high-pressure, hot, dense fluids.

So, while the outer planets are often referred to as "gas giants," they actually have a more complex composition that includes both gases and ices.