What group of crustaceans often fouls ships’ bottoms?

there are so many examples for that in different areas, like biology experiment carried out in our lab recently.

here's one link:

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