Final answer:
The option that is not a physical characteristic of blood is 'Sweet taste'. Blood is sticky, opaque, slightly alkaline, and more viscous than water, but it has a metallic taste, not sweet.
Step-by-step explanation:
To answer the student's question, among the listed options, the one that is not a physical characteristic of blood is 'd) Sweet taste'. Blood has a metallic taste due to the iron content in hemoglobin, not a sweet taste. To clarify the other options: Blood is indeed sticky, opaque, and heavier and more viscous than water. Blood is also slightly alkaline, not acidic, with a pH typically between 7.35 and 7.45.