<P> Elemental chlorine is extremely dangerous and poisonous for all lifeforms, and is used as a pulmonary agent in chemical warfare; however, chlorine is necessary to most forms of life, including humans, in form of chloride ions . </P> <P> Argon has no biological role . Like any gas besides oxygen, argon is an asphyxiant . </P> <Table> <Tr> <Th_colspan="19"> (hide) <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> Period 3 in the periodic table </Th> </Tr> <Tr> <Th> </Th> <Th> </Th> <Th> </Th> <Th> </Th> <Th> </Th> <Th> 5 </Th> <Th> 6 </Th> <Th> 7 </Th> <Th> 8 </Th> <Th> 9 </Th> <Th> 10 </Th> <Th> 11 </Th> <Th> 12 </Th> <Th> 13 </Th> <Th> 14 </Th> <Th> 15 </Th> <Th> 16 </Th> <Th> 17 </Th> <Th> 18 </Th> </Tr> <Tr> <Th_colspan="3"> Group → </Th> </Tr> <Tr> <Th_colspan="3"> ↓ Period </Th> </Tr> <Tr> <Th> </Th> <Td> Sodium 11 Na </Td> <Td> Magnesium 12 Mg </Td> <Td_colspan="10"> </Td> <Td> Aluminium 13 Al </Td> <Td> Silicon 14 Si </Td> <Td> Phosphorus 15 P </Td> <Td> Sulfur 16 S </Td> <Td> Chlorine 17 Cl </Td> <Td> Argon 18 Ar </Td> </Tr> <Tr> <Td_colspan="19"> </Td> </Tr> <Tr> <Td_colspan="19"> <Table> <Tr> <Td> <Table> <Tr> <Td> 1 (red) = Gas </Td> <Td> 3 (black) = Solid </Td> <Td> 80 (green) = Liquid </Td> <Td> 109 (gray) = Unknown </Td> <Td> Color of the atomic number shows state of matter (at 0 ° C and 1 atm) </Td> </Tr> </Table> </Td> </Tr> <Tr> <Td> <Table> <Tr> <Td> Primordial </Td> <Td> </Td> <Td> From decay </Td> <Td> </Td> <Td> Synthetic </Td> <Td> Border shows natural occurrence of the element </Td> </Tr> </Table> </Td> </Tr> <Tr> <Td> <Table> <Tr> <Td_colspan="10"> Background color shows subcategory in the metal--metalloid--nonmetal trend: </Td> </Tr> <Tr> <Td_colspan="6"> Metal </Td> <Td> Metalloid </Td> <Td_colspan="3"> Nonmetal </Td> </Tr> <Tr> <Td> Alkali metal </Td> <Td> Alkaline earth metal </Td> <Td> Lanthanide </Td> <Td> Actinide </Td> <Td> Transition metal </Td> <Td> Post - ​ transition metal </Td> <Td> Polyatomic nonmetal </Td> <Td> Diatomic nonmetal </Td> <Td> Noble gas </Td> </Tr> </Table> </Td> </Tr> </Table> </Td> </Tr> </Table> <Tr> <Th_colspan="19"> (hide) <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> Period 3 in the periodic table </Th> </Tr>

What element is in period 3 group 2