The chemical term selenious acid, synonymously used for selenous acid

The chemical compound selenous acid (H2SeO3, or more detailed: SeO(OH)2) is the selenium analogue of sulfurous acid (SO(OH)2), containing one selenium atom in its molecule instead of the sulfur atom in the latter. The term selenous acid is the common name for this compound, but the spelling selenious acid has also been used in the literature.
The name based on the systematic additive nomenclature is dihydroxidooxidoselenium [1].
Selenous acid is used, for example, in its isotopically labeled form (H2[⁷⁵Se]O3) as a reagent in the preparation of ⁷⁵Se-labeled cells for studies on selenium metabolism in human T-cells [2].

Note: Selenous acid should not be confused with selenonic acid, which has the same brutto formula as selenous acid, but a different structural formula, SeHO2(OH), with the systematic additive name hydridohydroxidodioxidoselenium [1].

Keywords: inorganic chemistry, biochemistry, nomenclature, synonyms, different spellings of chemical compound names

IUPAC reference
[1] N. G. Connelly, T. Damhus, R. M. Hartshorn and A. T. Hutton (preparators): Nomenclature of Inorganic Chemistry • IUPAC Recommendations 2005. RSC Publishing, Cambridge, UK, 2005; Table IR-8.1, page 130.

Selected references using the name selenious acid
[2] V. N. Gladyshev, K.-T. Jeang and T. C. Stadtman: Selenocysteine, identified as the penultimate C-terminal residue in human T-cell thioredoxin reductase, corresponds to TGA in the human placental gene. Proc. Natl. Acad. Sci. USA June 1996, 93, pp. 6146-6151. Abstract.
[3] H. E. Ganther: Selenotrisulfides. Formation by the reaction of thiols with selenious acid. Biochemistry 1968, 7 (8), pp. 2898-2905. DOI: 10.1021/bi00848a029.

Selected references using the name selenous acid
[4] F. S. Grimaldi and M. M. Schnepfe: Semimicrodetermination of Tantalum with Selenous Acid. Anal. Chem. 1958, 30 (12), pp. 2046-2049. DOI: 10.1021/ac60144a056.
[5] J. Milne: Chemical shift references for ⁷⁷Se NMR spectroscopy. Selenous acid. Magn. Reson. Chem. April 2005, 31 (7), pp. 652-655. DOI: 10.1002/mrc.1260310709.