Skeletal formula challenge

Shown structure: count the atoms in the drawing. Hidden structure: use the description to work out the molecular formula. Type ordinary letters and numbers. Press Enter to check, then Enter for the next question.

Hidden structure has no picture or compound name to reveal. Its clues determine a molecular formula; different structures may fit. Starter uses rings, C=C bonds, alcohols and halogens. Later levels add carbonyls, nitrogen and aromatic rings. Stretch includes group ratios and hydrogen-uptake data. The explanation stays closed until you open it.

Practice has no time limit. Quick 10 finishes after ten answers. In Time attack, the clock starts when the first question is ready and keeps running between questions and when you switch tabs. An incorrect answer scores zero. Streak tracks your longest run of correct answers.

Classroom view enlarges the question and adds Reveal answer. Classroom and teacher previews stay out of personal results. Use Fullscreen for a projector.