Final answer:
Iodine sticks to the fats & oils in the latent fingerprints. These fats, often unsaturated, react with iodine similarly to how unsaturated fats do in the iodine value test, which measures the unsaturation level in fats and oils. Therefore, the correct option is C .
Step-by-step explanation:
Iodine sticks to fats & oils present in the latent fingerprints. The process is somewhat similar to how iodine interacts with unsaturated fats in the iodine value test. Unsaturated fats have double bonds that are reactive towards halogens like iodine. In a similar fashion, the unsaturated fatty acids found in the sebaceous secretions on the skin's surface, which are transferred onto surfaces when touched, will react with iodine vapor during the fingerprint development process. Fatty acids along with amino acids, salts, and water make up the composition of a latent fingerprint residue. When iodine comes in contact with these residues, especially the fats and oils, it is temporarily absorbed, making the print visible.