History of up-date[version 2.5 to final version at 12th July, 2021]
Revision
Solution for Question 1-3 in Problem 1: The calculated value of NA was corrected to 6.07
× 1023.
Typo in the equation to define 1 m in Problem 1 (above Question 2-2) was corrected.
Problem 5: For the calculation of the number of cases for Figure 1, 10 indistinguishable
molecules → 10 molecules
Solution for Question 7 in Problem 5: associated with expansion → by removing theboundary wall
Explanation of bird’s-eye view in Problem 6: The figure → Figure 2
Solution for Question 1-3 in Problem 14: change the numbering of the solution to that ofthe problem
Question 4 in Problem 31: Duplicated sentence was removed.
[version 2.4 to 2.5 at 8th June, 2021]
Revision
Problem 4: standard entropies of formation → standard entropy changes
Solution for Question 1 in Problem 4: “92.4/60” was removed.
Solution for Question 8 in Problem 4: Figure was added, and the phrase “(see the rightfigure)” was inserted.
Solution for Question 9 in Problem 4: Problem 8 → question 8, and 3.55/2.27 →2.27/3.55
Question 3-2 in Problem 20:The standard Gibbs energy change for the water-splitting reaction is 237 kJ mol‒1.
→ The standard Gibbs energy change for the splitting of 1 mole of water is 237 kJ.
[version 2.3 to 2.4 at 7th April, 2021]
Correction of wording
Problem 26: Facial chirality → Planar chirality.
Revision in Advanced Difficulty

Facial chirality → Chirality.
[version 2.2 to 2.3 at 29th March, 2021]
Corrections
Henderson−Hasselbalch equation in Equations was corrected.
Question 5 in Problem 12: The value of CC-A was corrected (–106.0 mM → –105.0 mM).
[version 2.1 to 2.2 at 15th March, 2021]
Changes for the remote IChO
Date of IChO2021 in the cover page: 24th July → 25th July
Appendix part was added at the end of the the documents. Practical Tasks were moved toAppendix part, and the comment for this change was added as the Appendix to the Preface.
Only theoretical subjects were left in the Advanced Difficulty. The list of Advanced Skills
was moved to the Notes. Experimental techniques that do not appear in the Practical Tasks
in the IChO were removed.
Corrections
Question 1-2 in Problem 1: The definition of u was corrected.

NA was removed fromthe sentence of the question.
Solution for Question 1-2 in Problem 1: The equation and the answer were corrected
Solution for Question 8 in Problem 4: The equations for the calculation of the density ofgraphite and diamond were corrected.
Resonance structures of benzene in Problem 8 was corrected.
Electron–delocalized structure of anthracene for Question 2 in Problem 8 was corrected.
Chemical structure of ethylammonium nitrate in Problem 9 was corrected.
Label for R2-CO-NHS in equation S1 in Problem 9 was corrected.
Solution for Question 2 (2) in Problem 10: The equations to calculate [A2−]BTB and[HA−]BTB were corrected.
Problem 15: specific weight → density
Problem 19: ΔH → ΔHº and ‘⇄’ → ‘⇌’
Introduction for Question 8 in Problem 21: hydroxide → hydroxy
Solution for Question 2 in Problem 26: The structures of H-3 and H-4 were corrected.
Solution for Question 6 in Problem 28: The values of K, a, and [free[6]CPP] werecorrected.
[version 2.0 to 2.1 at 15th February, 2021]
Fixation of Typos
Question 6-3 in Problem 3: 𝐾! 𝑃" ≪ 1 → 𝐾! 𝑃! ≪ 1
Caption of Figure 1 in Problem 6: Potetinal → Potential
Solution for Question 13 in Problem 4: 𝐸#$% → 𝐸#$+"+"

Solution for Question 14 in Problem 4: 𝐴&,()% exp -− ,-! / → 𝐴&,(% exp -− ,-! /Changes in Wording
Question 9 in Problem 5: calculate → estimate
pipet → pipette in Task 6.
Addition
Question 2 in Problem 5: Here both N and n* are integers.
Aesthetic Changes
Change of indent/line-spacing in Constants, Problem 7 and Problem 14.
Minor improvement of Scheme in Problem 21.
Improvement of quality of Schemes in Problems 23 and 25.
Spacing between Figures in Problem 28.
Removal of pale shading on compounds in Tasks 4, 5 and 7.