<Tr> <Th> Ar </Th> <Td> syn </Td> <Td> 32.9 y </Td> <Td> β </Td> <Td> </Td> </Tr> <Tr> <Td_colspan="2"> <Ul> <Li> view </Li> <Li> talk </Li> <Li> </Li> </Ul> references in Wikidata </Td> </Tr> <Ul> <Li> view </Li> <Li> talk </Li> <Li> </Li> </Ul> <P> Argon is a chemical element with symbol Ar and atomic number 18 . It is in group 18 of the periodic table and is a noble gas . Argon is the third-most abundant gas in the Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as abundant as water vapor (which averages about 4000 ppmv, but varies greatly), 23 times as abundant as carbon dioxide (400 ppmv), and more than 500 times as abundant as neon (18 ppmv). Argon is the most abundant noble gas in Earth's crust, comprising 0.00015% of the crust . </P>

What is the coordination number of argon in solid argon