valence

What’s on the USNCO exam

Both the local section exam and national Part I are 60 multiple-choice questions, and both walk through the same ten topics in the same order, six questions at a time. Knowing which block a question number belongs to is worth real points: you always know what is coming next.

The exam

Question count
Local section exam60 multiple choice · 110 minutes · taken at your school or section in March60
National exam, Part I60 multiple choice · 90 minutes · ten blocks of six, in topic order60
National exam, Part II8 free-response problems · 105 minutes · graded against a rubric8
National exam, Part III2 laboratory problems · 90 minutes · practical work, not covered here2

Topics, by how hard they really are

Hardest first
Organic and biochemistryQuestions 55–60 · 134 in the bank38%EquilibriumQuestions 31–36 · 137 in the bank43%Bonding and molecular structureQuestions 49–54 · 136 in the bank44%Atomic structure and periodicityQuestions 43–48 · 136 in the bank47%Oxidation and reductionQuestions 37–42 · 136 in the bank47%Descriptive and laboratoryQuestions 7–12 · 134 in the bank50%States of matterQuestions 13–18 · 138 in the bank50%ThermodynamicsQuestions 19–24 · 134 in the bank52%KineticsQuestions 25–30 · 137 in the bank56%Stoichiometry and solutionsQuestions 1–6 · 132 in the bank64%

The percentage is the share of national qualifiers who answered correctly, from the item statistics ACS publishes with the national answer key, averaged over the 406 questions that carry one. Qualifiers are already a strong group, so a block where they average 38% is genuinely hard, not merely unfamiliar.

Every one of the 1,354 questions below is from a past exam, tagged to its block. Start practicing and the next question is chosen from whichever block you are weakest in.