Sg was classified based on its physical properties and chemical composition.
The correct answer to the given question is option a).
The classification of Sg is based on its physical properties and chemical composition. By looking at the color, texture, grain size, sorting, and depositional environment, we can determine the classification of a rock sample.
For example, if Sg is classified based on its physical properties, we can observe its color and size. If it is classified based on its chemical composition, we can analyze the elements present in Sg.
Therefore, option a) is the correct classification for Sg.