2026 · Paper 1 · Chemistry
Question 2
The printed question, the official key, and each model’s JSON answer plus the reasoning it wrote.
ChemistryPaper 1Single correct
Q02
Official C
Model answers
Claude Fable 5.1
Anthropic
Correct3 / 3
C
Claude Fable 5.1 reasoning
At equilibrium, K = kf/kb = 1/4 = [P]eq/[R]eq. With [R]+[P]=[R]0, [R]eq/[R]0 = 0.8 and [P]eq/[R]0 = 0.2. This matches option (C).
GPT 6 Astra
OpenAI
Correct3 / 3
C
GPT 6 Astra reasoning
No written reasoning was returned for this item.
GPT 5.5
OpenAI
Correct3 / 3
C
GPT 5.5 reasoning
No written reasoning was returned for this item.
Claude Sonnet 5
Anthropic
Correct3 / 3
C
Claude Sonnet 5 reasoning
Setting kf[R]=kb[P] at equilibrium gives [P]/[R]=1/4, so [R] settles at 0.8 and [P] at 0.2 of the initial concentration — matching option C.