Sub-topic 1
2024 · National One-Eighth
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Riddle: carbon-12
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Sub-topic 2
2003 · National Semifinal
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Identifying the periodic table group of an element from its atomic number
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Sub-topic 3
2013 · National Preliminary
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Riddle: sodium as a group 1 metal that tarnishes and reacts with chlorine
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Sub-topic 4
2013 · National Preliminary
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Why chromium's ground-state configuration is 4s1 3d5 rather than 4s2 3d4
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Sub-topic 5
2021 · National Quarterfinal
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Helium is preferred over argon for balloons because it is far less dense
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Sub-topic 6
2023 · National Preliminary
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True or false: atomic number does not track density or order of discovery
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