Final answer:
The shape of a clay particle is flat plate-like, which gives clay its unique characteristics such as plasticity when wet and hardens when dry.
Step-by-step explanation:
Clay particles have a flat plate-like shape, which is option C in the choices provided. These flat plate-like particles contribute to the characteristic physical properties of clay, such as its plasticity when wet and its ability to form a hard mass when dried or fired. Unlike shapes that are squamous flat, irregular round, cuboidal, or tall and narrow cells, which refer to the morphology of biological cells, clay particles are mineralogical and have a distinct plate-like structure. This structure of clay particles varies depending on the mineral composition, but they do not have a round, long, or undefined shape as other options might suggest.