What is the form of liquid chromatography used to separate compounds that are dissolved in solution?

High-Performance Liquid Chromatography (HPLC) is the correct answer as it is specifically designed for separating, identifying, and quantifying compounds that are dissolved in a liquid solution. HPLC utilizes a high-pressure pump to push the solvent (mobile phase) through a column filled with stationary phase materials. This allows for the rapid and efficient separation of different compounds based on their interactions with the stationary phase, making it highly effective for complex mixtures.

HPLC is widely used in various fields such as pharmaceuticals, biotechnology, and environmental analysis due to its high resolution, sensitivity, and ability to analyze very small sample volumes. The technique can be executed with various types of detectors, enhancing its versatility for diverse analytical applications.

Other forms of chromatography mentioned are generally used for different purposes or types of samples: gas chromatography is mainly for volatile compounds and gases, thin-layer chromatography is primarily used for quick, qualitative analysis of small sample sizes, and paper chromatography is often employed for educational demonstrations or the separation of less complex mixtures. These methods do not typically handle the same range of applications or the specific requirements for liquid samples as effectively as HPLC.