Final answer:
Heparin is the anticoagulant that prevents platelets from clumping and preserves the appearance of blood cells for microscopic preparation.
Step-by-step explanation:
The anticoagulant that prevents platelets from clumping and preserves the appearance of blood cells for microscopic preparation is Heparin. Heparin is a short-acting anticoagulant that opposes the conversion of prothrombin to thrombin, and it is found on the surfaces of cells lining the blood vessels. It is commonly used in surgical patients at risk for blood clots.