What is the most common rock on earth

That would be igneous rock. Igneous rock is formed by the cooling of molten rock (magma and/or lava). Since there is such and abundance of liquid rock on Earth, it makes igneous rock the most common TYPE of rock.

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answer; the tunica intima also called tunica interna, consists of elastic fibers,connective tissue and smooth muscle cells;

hydrogen is a compound or a single element and a element is a pure substence that cannot be separated into simpler subtances

clorine is a compound its a chemical substance that forms when two or more different elements combine

so both hydrogen and clorine are compounds