The part of a solar cooker responsible for the greenhouse effect is the (c) glass sheet.
Explanation: The greenhouse effect occurs when sunlight enters a transparent material like glass, is absorbed by the surfaces inside, and then re-radiated as heat, which is trapped within the material.
Why other options are incorrect:
(a) Coating with black colour inside the box:
While the black coating absorbs sunlight efficiently, it’s the glass sheet that traps the heat generated.
(b) Mirror:
The mirror’s function is to concentrate sunlight onto the cooking area. It doesn’t trap the heat like the glass sheet does.
(d) Outer cover of the solar cooker:
The outer cover usually provides insulation to minimize heat loss, but it’s the transparent glass sheet that creates the greenhouse effect.