**Category:** Inorganic Chemistry  
**Subtype:** Chemical Reactions and Stoichiometry  
**Problem Description:** This problem involves a mixture of iron compounds reacting with a potassium hydrogen sulfate solution, leading to the formation of a neutral salt and nitrogen monoxide gas. It also includes a subsequent reaction with sodium hydroxide and the determination of the maximum mass of copper that can be dissolved in the resulting solution. The goal is to find the mass \( m \) of copper that can be dissolved.