Trained dogs are able to track people by detecting certain compounds in their sweat. The correct compound that dogs recognize in sweat is carboxylic acids. This compound is present in the sweat that is released from the feet. Trained dogs are able to distinguish this compound and recognize it as a specific scent that they can follow.

Option 2, uric acid, is not the correct answer. While uric acid is indeed present in sweat, it is not the compound that dogs specifically recognize when tracking individuals.

Option 3, sugar, is also not the correct answer. While sugar is found in sweat, it is not the compound that dogs rely on for tracking purposes.

Option 4, salt, is not the correct answer either. While salt is present in sweat, it is not the specific compound that dogs use to track people.

Therefore, the correct answer is option 1, carboxylic acids, because it is the compound in sweat that trained dogs recognize and use for tracking individuals.