A polyhedron is a solid shape with many sides. The word "polyhedron" does not specify a number of sides.
A cuboid would fit the given description
To make solid colored paint keep stirring until the marbleized effect stops. Make sure to get all sides and the bottom as well.
Without the thickness of the rock it is difficult to know. It would likewise be necessary to know what type of stone.
A wide range of values in art refers to the use of many values of light. A value scale is the easiest way to visualize this. Make 10 small squares on a page. Square 1 is solid black, square 10 is complete white, all squares in between become progressively lighter (towards the white end) or darker (the black end). This 10 square scale is a small range of values.
A pyramid
a cube
No because it is flat 2d shape with 4 equal sides
Cube, aka hexahedron
Not necessarily. The solid could be a square based cuboid (hexahedron).
The figure is a pyramid and the base is a square.
There is a contradiction in your question. If the base has four equal sides then is it a square so not all the faces are Triangles. However if the base is a square and the rest of the faces are triangles then your object is a "Square-based Pyramid"
A pyramid. The square being the base and the triangles the 'sides' - each having a side connected to a side of the square - the other sides connected to 'neighbor-triangles'.
Four Right angles are in a solid square because a square has four sides
A cube.
a Dodecahedron is a 3 diamentional shape having 12 plain faces in a regular solid figure with 12 equal pentagonal sides!
CUBE