The 1991 one rupee belongs to the Wheat Ears definitive series of Republic India. Its reverse carries the stylised wheat-ear design that defined circulating one-rupee coinage of that era, making it a familiar yet keenly collected date.
Coins from this series draw interest because condition varies enormously across the many millions that once circulated; well-struck, lustrous examples in the higher grades are far scarcer than worn pieces, and small die differences can matter to specialists. As always, value depends on the exact year, mint and preservation, so an uncirculated coin sits well above a used one.
On Coinbazzar each 1991 one rupee is listed by a verified seller with clear images, so you can judge the grade before you buy. See the live listing on this page for the current asking price.