We report the results of our studies on the optical and thermal properties of the mixture of 4-cyano-4 '-octyloxybiphenyl (80CB) and N-Cetyl-N, N, N, trimethyl ammonium bromide (CTAB) + Glacial acetic acid (GAA), which exhibits a very interesting lower temperature reentrant nematic and smectic-A phases, sequentially when the specimen is cooled from its isotropic liquid phase. The different phases of these mixtures are identified using optical and microscopic techniques. The temperature variations of optical anisotropy, Ultrasonic velocity, molar compressibility, and adiabatic compressibility have been also discussed.