A

Step 1: Understand the purpose of a calorimeter. It is used to measure the heat transfer during chemical reactions or physical changes.
Step 2: Metal has a high thermal conductivity compared to glass. This means it can quickly transfer heat between the substance inside the calorimeter and the surrounding environment.
Step 3: The rapid heat transfer ensures accurate measurement of the temperature change, which is critical to calculating heat flow. Glass, on the other hand, is an insulator, leading to slower heat transfer and less accurate results.
Step 4: Additionally, metals are typically more durable and less prone to breakage compared to glass, making them more practical for laboratory use.
Conclusion: Therefore, calorimeters are made of metal to ensure efficient heat transfer and durability.