In classical conditioning, Conditioned and Unconditioned Stimulus are mentioned. In Pavlov’s description these Conditioned and Unconditioned Stimulus are mentioned again and again. Unconditional stimulus was is responsible for all the natural responses. Conditioned stimulus is based on and much related to the unconditioned ones. For example, hunger is an unconditional stimulus and we feel hungry due to that. It is purely an unconditional stimulus. Smell of a food creates a desire for that particular food. It is an example of unconditional stimulus. This is not directly related to hunger but it definitely increases the hunger of an individual (BinKhamis, Léger, Bell, SPrendergast, O’Driscoll, & Kluk, 2019).