Methyl Red Sodium Salt is a pH indicator used in microbiology and biochemistry to determine the acidity or alkalinity of solutions, exhibiting a color change from red to yellow in the pH range of 4.2 to 6.2. The sodium salt form provides enhanced water solubility compared to the free acid. It is commonly applied in culture media to detect pH changes from microbial metabolism, aiding bacterial identification, especially in the Methyl Red Test for acid production during sugar fermentation (e.g., in Escherichia coli). Additionally, it is used in acid-base titrations and environmental testing for water quality and pollution assessment. Its stability and sharp color transition ensure reliability in laboratory analyses.