Final answer:
A: Styrofoam.
The calorimeter used at constant pressure in chemistry labs is the Styrofoam or coffee-cup calorimeter, which is used for monitoring heat flow in solution-based processes.
Step-by-step explanation:
Calorimeters in a Chemistry Lab
The type of calorimeter used at constant pressure in chemistry labs is the Styrofoam calorimeter, also known as the coffee-cup calorimeter.
These are simple calorimeters often constructed from polystyrene cups, designed to measure heat flow in processes that occur in solution at atmospheric pressure. They are not as accurate as bomb calorimeters which operate at constant volume and are used for reactions that yield large amounts of heat and gas, such as combustion.
The Styrofoam calorimeter helps in measuring changes in temperature and allows for the determination of energy changes in various chemical processes.