a substance that is dissolved in another substance\nantibodies\nsolutions\nantigens\nsolute\nskin…

Brief Explanations:

A solute is defined as a substance that gets dissolved in another substance (a solvent) to form a solution. Antibodies are proteins in the immune - system, solutions are the mixture formed, antigens trigger immune responses, skin turgor is related to skin elasticity, and a catheter is a medical device.

Answer:

solute