Subscript Three

Subscript Three at U+2083 is a small baseline-lowered digit used when the number 3 is part of a subscript rather than ordinary text. It belongs to the Superscripts and Subscripts block and is meant for plain-text notation where true mathematical or typographic formatting is not available. Its most common real-world use is in chemistry, where it marks atom counts in formulas such as NH₃ for ammonia, O₃ for ozone, and Fe₂O₃ for iron(III) oxide. It is also useful in physics and mathematics for indexed variables, such as x₃ for the third component of a vector, a₃ for the third term of a sequence, or H₃ in a family of named quantities. In technical notes, databases, filenames, and messaging, ₃ lets people preserve subscript meaning without rich-text layout. It should not be confused with a styled normal digit: searches, sorting, and calculations may treat it as a distinct character rather than the number 3.