(i) 3 triangles?

No, Because a polyhedron is a solid shape bounded by polygons.

(ii) 4 triangles?

Yes, Because four triangles will form a tetrahedron, which is a polygon.

(iii) a square and four triangles?

Yes, because a square pyramid has a square and four triangles as its faces. Since pyramid is a polyhedron whose base is a polygon of any number of sides and whose other faces are triangles with common vertex.