Which planet is characterized by having a giant red spot and is composed primarily of hydrogen?

The planet characterized by having a giant red spot and being composed primarily of hydrogen is Jupiter. This distinctive feature, known as the Great Red Spot, is a massive storm that has been raging for hundreds of years, showcasing Jupiter's dynamic atmosphere.

Jupiter is classified as a gas giant, which means it is primarily made up of hydrogen and helium with traces of other elements. This composition is a defining characteristic of gas giants, distinguishing them from terrestrial planets, which have solid surfaces. The presence of the Great Red Spot and the planet's thick atmosphere hints at the complex meteorological phenomena that take place there, driven by the extreme pressure and temperature conditions found in its upper atmosphere.

In contrast, Saturn, while also a gas giant and largely composed of hydrogen, does not feature a storm of comparable prominence to the Great Red Spot. Mars, being a terrestrial planet, is primarily composed of rock and metal, lacking the gaseous characteristics that define gas giants. Uranus, although an ice giant with a significant amount of hydrogen, is not known for a similar giant storm feature.