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Reference

Periodic table, formulas & constants, and external resources for USNCO prep.

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Exam & registration

Official exam info, eligibility, dates.

ACS USNCOOfficial exam info & registration
IChO OfficialInternational olympiad rules & dates

Past papers

Real problems from past USNCO + UK olympiads.

IChO Past PapersIChO problems archive
UK Chemistry OlympiadRSC past papers & solutions

Lookups & help

Reference data + community help when you're stuck.

NIST WebBookThermodynamic & spectral data lookup
ChemLibreTextsFree general chemistry textbook
Chemistry Stack ExchangeQ&A for tricky concepts