Assuming there was a body of water large enough to hold it, of course. Saturn, the famous ringed gas giant of our solar system, consists of an iron, nickel, and rock core surrounded by a metallic hydrogen layer. It has a middle layer of hydrogen and helium in their liquid forms, followed finally by an outer layer of gaseous hydrogen and helium with trace amounts of compounds like ammonia, acetylene, ethane, and more. The atmosphere contains 96.3% hydrogen and 3.25% helium, and gives the planet a mean density of 0.687 g/cm^3.
For comparison, the gas giant Jupiter has a mean density of 1.326 g/cm^3, Uranus 1.27 g/cm^3, and Neptune 1.638 g/cm^3. Sadly, all three would sink in our hypothetical body of water. Via Saturn