Chromium does not have magnetic properties so it cannot be separated by magnetic separation.

**Explanation:**

Magnetic separation is a method used to separate magnetic materials from non-magnetic ones. It relies on the magnetic properties of the materials being separated. When a mixture of magnetic and non-magnetic materials is passed through a magnetic field, the magnetic materials are attracted and separated from the non-magnetic ones.

Among the given options, **steel, nickel, cobalt, and chromium** are all magnetic materials and can be separated using magnetic separation. However, **chromium** cannot be separated by magnetic separation.

**Reason:**

Chromium is a chemical element with the symbol Cr and atomic number 24. It is a lustrous, hard, and brittle metal that possesses high corrosion resistance. Unlike steel, nickel, and cobalt, chromium is not ferromagnetic, meaning it does not possess a permanent magnetic moment. Ferromagnetic materials are strongly attracted to magnets and can be magnetized themselves. Non-ferromagnetic materials, on the other hand, are weakly attracted to magnets or are not attracted at all.

While chromium does exhibit some weak paramagnetic properties (which means it is weakly attracted to magnets), it does not possess a strong enough magnetic moment to be effectively separated using magnetic separation techniques. Therefore, chromium cannot be separated by magnetic separation.

It is important to note that magnetic separation is just one of many methods used for separating scrap metals. Other techniques such as gravity separation, flotation, and electromagnetic separation are also commonly employed depending on the specific properties of the metals being separated.

Chromium does not have magnetic properties so it cannot be separated by magnetic separation.