Final answer:
Chemical antagonism is an interaction between an agonist and an antagonist. An agonist activates a receptor, while an antagonist blocks the receptor.
Step-by-step explanation:
Chemical antagonism is an interaction between an agonist and antagonist. An agonist is a molecule that binds to a receptor and activates it, while an antagonist is a molecule that binds to a receptor but does not activate it, thus blocking the agonist from binding. For example, in the context of neurotransmitters, an agonist mimics a neurotransmitter and activates a receptor, while an antagonist blocks the receptor and prevents the neurotransmitter from binding.