Final answer:
Nitrogen is the chemical substance not found in carbohydrates; carbohydrates are composed of carbon, hydrogen, and oxygen.
Step-by-step explanation:
The chemical substance not found in carbohydrates is nitrogen. Carbohydrates are a class of organic compounds that contain three elements: carbon, hydrogen, and oxygen. These are the basic building blocks that form carbohydrates in a ratio that usually approximates (CH2O)n, where 'n' is the number of units forming the carbohydrate molecule. Common examples of carbohydrates include sugars like glucose and fructose, as well as larger molecules like starch and cellulose.