This question depends on what importance is being assigned. The most common dissolved ions (elemental atoms do not dissolve) are sodium and chloride, but they are many other important elements found in sea water.
The two elements that make up most of the oceans are hydrogen and oxygen, forming water molecules.
The two most common elements in the Universe, and in most stars are - in that order - hydrogen and helium (elements #1 and #2).
Oxygen and silicon are the two most abundant elements found in the most common minerals. The most common minerals found on Earth are silicates.
The two most common elements found in nebulas are hydrogen and helium. These elements are the building blocks of stars and galaxies, and are formed during the process of stellar nucleosynthesis.
Hydrogen and Helium are the two most common elements in the universe.
Water (H2O) and salt (NaCl).
Hydrogen and helium.
Oxygen & Silicone.
Hydrogen, followed by helium.
Dirt and Dirt!
Nitrogen and oxygen are the two most abundant gases in the air. They are actually elements and not compounds. The two most abundant compounds would be water vapor and carbon dioxide.
the most common element is hydrogen and its molecule of two hydrogen atoms is the most common molecule