Final answer:
Ninhydrin is the reagent used to develop latent fingerprints on porous materials as it reacts with amino acids in sweat to form a purple-blue compound.
Step-by-step explanation:
The chemical reagent commonly used to develop latent fingerprints on porous materials such as paper is Ninhydrin. Ninhydrin reacts with the amino acids that are present in the sweat residues of fingerprints to produce a purple-blue colored complex known as Ruhemann's purple. The strong visual contrast of this color allows for the clear visualization of latent fingerprints on porous surfaces. Since ninhydrin reacts due to amino groups, it is particularly effective for this purpose. Other reagents mentioned, such as Silver nitrate, Iodine fuming, and Cyanoacrylate, are used for developing fingerprints on different types of surfaces and under different conditions.