These are the 5 convex regular "solids" made out of identical regular polygons.
They are:

The Tetrahedron. ( 4 triangular sides, 4 corners )

The Octahedron ( 8 triangular sides, 6 corners )
dual to
The Cube ( 6 square sides, 8 corners )

The Icosahedron
( see French and London  versions )
( 20 triangular sides, 12 corners )
dual to
 The Dodecahedron ( 12 pentagonal sides, 20 corners )

Test: Which of the following models is not a platonic solid ? >>>