Density, Refractive Index, and Speed of Sound of the Binary Mixture of 1-Butyl-3-methylimidazolium Tetrafluoroborate + N-Vinyl-2-pyrrolidinone from T = (298.15 to 323.15) K at Atmospheric Pressure Sunkara, G.R.; Tadavarthi, M.M.; Tadekoru, V.K.; Tadikonda, S.K.; Bezawada, S.R.; Journal of Chemical & Engineering Data 2015, 60, 886-894