ANS:C - T²

The drying time between fixed moisture content within the diffusion-controlled "falling rate period" is proportional to 𝑇2T2 (where 𝑇T is the thickness of the solid). During the falling rate period of drying, moisture removal from the material is primarily governed by internal diffusion of moisture through the material to its surface. This process involves moisture traveling from the interior of the material to the surface, where it evaporates into the surrounding air. The rate of diffusion is proportional to the square of the thickness of the solid (𝑇2T2). This is because the time it takes for moisture to diffuse through a solid material is directly related to the distance it needs to travel. As the thickness of the material increases, the diffusion path becomes longer, resulting in a proportional increase in drying time. Therefore, the drying time between fixed moisture content within the diffusion-controlled falling rate period is proportional to 𝑇2T2.