Why is sodium hydroxide used in the identification of certain metal ions?

Sodium hydroxide is used in the identification of certain metal ions because it forms colored precipitates with some metal ions. When sodium hydroxide is added to a solution containing metal ions, it can react to form insoluble metal hydroxides. The particular color of the precipitate can help indicate which metal ion is present in the solution. For example, copper(II) ions will produce a blue precipitate of copper(II) hydroxide, while iron(III) ions will yield a brown precipitate of iron(III) hydroxide. This characteristic formation of colored precipitates is a key aspect of qualitative analysis in chemistry, aiding in the identification of the specific metal ions present in a sample.

The other options do not accurately describe the role of sodium hydroxide in this context. Sodium hydroxide does not react violently with metal ions (the first choice), nor is its primary purpose in this scenario to neutralize acids (the third choice) or to make solutions safer (the fourth choice).