Stainless steel is everywhere in our daily lives, and there are many different grades—many people often have trouble telling them apart. They may not know which grades are suitable for specific applications or which grade is considered high-quality.

Copper(I) is commonly referred to as cuprous copper; cuprous chloride (CuCl), cuprous oxide (Cu₂O), and cuprous sulfide (Cu₂S) are all common monovalent copper compounds. [Cu(NH₃)₂]²⁻ is a complex ion formed by cuprous copper and ammonia; it is colorless, easily oxidized, and spontaneously dissociates in acidic solutions to form Cu(II) and Cu.

Copper is a non-ferrous metal that plays a vital role in human life. It is widely used in the electrical, light industrial, machinery manufacturing, construction, and defense industries, and ranks second only to aluminum in terms of consumption among non-ferrous metals in China. Copper is a red metal, but it is also considered a “green” metal. It is called a “green” metal primarily because it has a low melting point, making it easy to remelt and re-smelt, and therefore relatively inexpensive to recycle.