Today on Nigma noticed the news:

Nigma finds chains of chemical reactions

I tested it, I regretted that in my time there were no such things yet. I remember in school the type of such puzzles were - fill in the blanks.

NaCl =? = NaH =? = NaHSO3


We were pleased with the cool system responses when no results were found:
H2O -> ... -> ... -> H3O

NaOH -> Na2SO4 -> ...

I remembered the phrase from the Pokrovskie Vorota film: “I’m all so sudden ... all contradictory ...”