Answer:
1. The tetrahedron has 4 vertices, 6 edges and 4 faces. Then V-E+F=4-6+4=2
2. The cube has 8 vertices, 12 edges and 6 faces. Then V-E+F=8-12+6=2
3. The octahedron has 6 vertices, 12 edges and 8 faces. Then V-E+F=6-12+8=2
4. The icosahedron has 12 vertices, 30 edges and 20 faces. Then V-E+F=12-30+20=2
5. The dodecahedron has 20 vertices, 30 edges and 12 faces. Then V-E+F=20-30+12=2.