The application of which type of solution is critical for the enhancement of latent prints on porous surfaces?

The enhancement of latent prints on porous surfaces is most effectively achieved through the application of Ninhydrin solution. Ninhydrin reacts with the amino acids present in the sweat and oils left behind in fingerprint residues. When this solution is applied to porous materials such as paper or cardboard, it develops prints by forming a colored compound known as Ruhemann's purple. This reaction is particularly beneficial because porous surfaces tend to absorb moisture, which can make accessing the latent prints difficult without a suitable chemical development method.

Other solutions listed may have their uses but are not specific to enhancing latent prints on porous substrates. For example, acidic and alkaline solutions may alter the surface properties of substrates or engage in chemical reactions unrelated to the proteins and amino acids in latent prints. Solvent-based solutions, while useful for non-porous surfaces or certain types of residues, would not effectively highlight the organic components found in porous substrates. Thus, Ninhydrin is the preferred choice for successfully developing latent prints from porous materials.