Liquids must be vaporized when using which of the following methods?

The correct approach emphasizes that when a chromatograph is being used, the analysis often involves separating different components of a mixture. Many chromatographic techniques, such as gas chromatography, specifically require that the sample be in a vaporized state to facilitate the separation of its components. This is essential because the retention time and interaction of substances with the stationary phase depend on them being in a gaseous state, which allows for accurate detection and analysis of the individual compounds present in the sample.

In contrast, measuring density typically involves liquids, and purity can sometimes be assessed without vaporizing samples. Conductivity measurements are usually conducted in the liquid state as well, where ions in solution contribute to the conductivity rather than requiring a vaporized state. Therefore, vaporization is a crucial step specifically in chromatographic methods to ensure effective separation and analysis of varied compounds.