Using the activity series provided. which reactants will form products?
na> mg> al> mn> zn> cr> fe> cd> co> ni> sn> pb> h> sb> bi> cu> ag
1. ag +nano3
2. fe + al2o3
3. ni + nacl
4. fe + cu(no3)2

The series of metals shown above is what we call the activity series. This is a guide for us to know what products are formed during a metal displacement reaction. A metal must be above the other metallic compound for displacement to occur. 

1. Ag is way below the series compared to Na. No reaction occurs.
2. Al  is above Fe, no reaction occurs. 
3. Na is above Ni, no reaction will occur. 
4. Fe is a more active metal than copper. A displacement reaction will occur.