Where is the coolest air found inside an oven

At the bottom

Explanation:

Air is a fluid. When a fluid is heated, such as in the oven, it undergoes convection: the part of the fluid which is heated more becomes less dense than the rest of the fluid (because the molecules move  faster, so the separation between them increases), so it moves on top of the fluid, while the colder parts of the fluid, being more dense, move on bottom. Then the colder parts of the fluid are also heated, and they move on top, and this process continues: we say that a convective current is created.

As we just described, therefore, the colder parts of the air remain at the bottom, since they are more dense than the hotter air.

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