Density (ρ), refractive index (n D ), and speed of sound (u) values are measured for the binary mixture of 1butyl-3-methylimidazolium tetrafluoroborate (1) and N-vinyl-2-pyrrolidinone (2) over the entire range of mole fractions at temperatures from T = (298.15 to 323.15) K under atmospheric pressure. Using the basic experimental data, various acoustic and thermodynamic parameters are calculated and are discussed in terms of molecular interactions between the present investigated binary system. The excess values are fitted to the Redlich−Kister polynomial equation to estimate the binary coefficients and standard deviation between the experimental and calculated values. Further, the molecular interactions in the binary mixture system are analyzed using the experimental FT-IR spectrum recorded at room temperature.