A sphere.
"Hedron" is usually at the end of a geometrical shape meaning "faces".
Three.
spiders do not build geometrical shape webs
Octagon
Geometrical symmetry is a mathematical term for a shape that, if torn in half, can be mirrored and restored to the shape again.
Yes. But any object is a geometrical shape of some sort. Even a blob is an irregular geometric shape!
We cannot assess the efficiency of a geometrical shape unless we have a particular purpose in mind. You will have to state what you wish to efficiently do, by means of a geometrical figure.
If you mean a round can, the shape is cylindrical.
A sphere
yes
Yes
Tetraedral