chlorous acid
Technical term in chemistry; refers to the inorganic acid HClO₂.
Chlorous acid is unstable and exists only in aqueous solution.
次亜塩素酸 (hypochlorous acid, HClO) has one less oxygen atom than 亜塩素酸 (chlorous acid, HClO₂).
塩素酸 (chloric acid, HClO₃) has one more oxygen atom than 亜塩素酸.
Compound of 亜 (a-, 'sub-') + 塩素 (enso, 'chlorine') + 酸 (san, 'acid'). The prefix 亜 indicates a lower oxidation state compared to 塩素酸.