What chemical process is used for obtaining a metal from its oxide?

Metallic oxide of zinc, magnesium and copper were heated with following metals :

In which case will you find displacement reactions taking place?

What are alloys?

Which of the following pairs will give displacement reactions?

1. NaCl solution and copper metal
2. MgCl₂ solution and aluminium metal
3. FeSO₄ solution and silver metal
4. AgNO₃ solution and copper metal.