Final answer:
Neutrophils are the leukocytes that can synthesize and release leukotrienes on demand.
Step-by-step explanation:
The leukocyte that is able to synthesize and release leukotrienes on demand is the neutrophil. Neutrophils are a type of granulocyte that are involved in the immune response to bacterial infections. They release leukotrienes, which are lipid mediators that help recruit other leukocytes to the site of infection and initiate an inflammatory response.