Final answer:
Osium tetroxide is the chemical typically used for fixation and staining in sample processing for transmission electron microscopy.
Step-by-step explanation:
The chemical typically used for fixation as well as staining in sample processing for transmission electron microscopy is osmium tetroxide. Osmium tetroxide is a strong fixative that helps preserve the ultrastructure of cells and tissues, making them suitable for TEM examination.
It also acts as a contrasting agent, enhancing the visibility of cellular components under the electron microscope.