<Ul> <Li> Nonmetals </Li> </Ul> <Ul> <Li> reactive nonmetals </Li> <Li> noble gases </Li> </Ul> <Tr> <Td> By other characteristics (show) <Ul> <Li> Coinage metals </Li> <Li> Platinum - group metals </Li> </Ul> <Ul> <Li> Precious metals </Li> <Li> Refractory metals </Li> </Ul> <Ul> <Li> Heavy metals </Li> <Li> Light metals </Li> </Ul> <Ul> <Li> Native metals </Li> <Li> Noble metals </Li> </Ul> <Ul> <Li> Main - group elements </Li> <Li> Rare - earth elements </Li> </Ul> <Ul> <Li> Transuranium, transplutonium elements </Li> </Ul> <Ul> <Li> Major, minor & trans - actinides </Li> </Ul> </Td> </Tr> <Ul> <Li> Coinage metals </Li> <Li> Platinum - group metals </Li> </Ul>

Which of the following is the outermost shell for elements of period 2