This is the smallest anion that can form multi-dimensional chain structures in a phenomenon called “dimensional caging.” A solution containing this anion can test for explosive peroxides in stocks of diethyl ether exposed to air. Sulfuric acid and a compound with this anion are the products of the Bunsen reaction used to produce hydrogen gas. Thiosulfate reacts with a mixture of manganese and this anion to quantify dissolved oxygen in the (*) Winkler method. Since this weakest ligand on the spectrochemical series resembles ice when bonded to silver, it is used to induce nucleation (10[1])during cloud seeding. (-5[1])The blue charge-transfer complexes (-5[1])formed by this monatomic anion make it a useful starch indicator. For 10 (10[1])points, name (-5[1])this anion (10[1]-5[1])that is the common form (10[1])of an element found in the thyroid. ■END■ (10[3])