Simple categories matching monoatomic:

• system,
• substance,
• fluid,
• gas,

Members with property monoatomic:

• he,
• argon,
• ar,
• cluster,
• hydrogen,
• neon,
• xe,
• oxygen,
• kr,
• nitrogen,
• krypton,
• helium,
• xe_kr,
• ne,
• xenon,
• ni,
• neon_gas,
• xenon_xe,
• krypton_gas,
• rare_gas,
• fe,
• cu,
• liquid_argon,