What is chemical stimuli

Chemical stimuli are molecules that cause a response at a cellular level primarily through cellular receptors. This happens all the time in nature - cells communicate with one another through chemical messaging. An example is an aroma molecule, such as the scent from a flower. This particular molecule is detected by the olfactory cells (those associated with the sense of smell) in your nose, producing a chemical reaction that ultimately leads to you consciously experiencing the smell.

Such a question like this could be looked up online (google) but i beleive its any process that results in the change in state or activity in a cell or organism