Crossword Clue:

pentavalent element or group

AnswerCrossword Clue
IRIDIUMPlatinum-group element
IODINElement of the halogen group.
CERIUMElement of rare-earth group.
HARDCOREUnyielding element of a group.
SODIUMElement of the alkali group.
OLDGUARDConservative element of a group.