What is one use of sodium hydroxide?

Sodium hydroxide, commonly known as caustic soda, plays a crucial role in the manufacture of bleach, specifically sodium hypochlorite, which is a key component in many household and industrial cleaning products. The reaction involves sodium hydroxide reacting with chlorine gas to produce sodium hypochlorite. This compound is renowned for its powerful bleaching and disinfecting properties, making it a popular choice for sanitation and cleaning applications.

In contrast, while sodium hydroxide is involved in various industrial processes, it is not primarily used in the direct manufacture of fertilizers, glass, or metals. Fertilizers often involve other compounds like ammonium nitrate or urea. The manufacture of glass typically utilizes silica sand, soda ash, and limestone rather than sodium hydroxide. In the context of metals, sodium hydroxide might be used in some processes, but it is not a primary agent in metal production. Thus, the most accurate and direct use of sodium hydroxide from the provided options is in the manufacture of bleach.