There is not a polyhedron with the given number of faces, edges and vertices.
Octahedron is the name of any shape with 8 faces. A hexagonal prism has your requirements.
then it's a - Dodecahedron
An octahedron is a polyhedron with eight faces, twelve edges, and six vertices
There is no 3-d shape with 4 and 1 = 5 triangular faces.
It is a triangular prism.
square based triangle
It is a cube or a cuboid which also has 12 edges and 8 vertices
The question is ambiguous. An octagon is a 2-dimensional shape with 8 edges and 8 vertices. Does a 3-D octagonal shape mean one with 8 edges or 8 faces or vertices, or faces which are 2d octagons?
A parallelepiped, of which a cube is a special case.