Project Hail Mary is filled with references to various chemical compounds. Here’s a few we’ve found:

water H₂O
carbon dioxide CO₂ (50 times as the words; 2 times hyphenated adjective; 15 times as the chemical formula)
ammonia NH₃ (36 times)
methane CH₄ (29 times)
ATP (adenosine triphosphate) (4 times)
DNA (deoxyribonucleic acid) (15 times)
glucose C₆H₁₂O₆ (2 times)
sulfur dioxide SO₂ (5 times)
sulfur hexafluoride SF₆ 14.150
sulfuric acid H₂SO₄ 21.284
heroin C₂₁H₂₃NO₅ (8 times)
Zylon poly(p-phenylene-2,6-benzobisoxazole) (2 times)

and of course

xenonite (124 times)

Let us know if we’ve missed any!