Counting only topologically distinct hydrogen environments (treat each chain CH2 as its own environment, and ignore the sodium ion), how many distinct hydrogen environments does the anion in the compound shown have? Give an integer.

The compound shown is sodium lauryl sulphate, anion C12H25OSO3-. The chain has CH3 (1), the OCH2 (1) and ten other CH2 groups, each topologically different from the others (no symmetry in an unbranched chain). Total 1 + 1 + 10 = 12, confirmed with RDKit canonical ranks.