Identifying Variable Composition Substances

Substances can be classified based on their composition. Some have a fixed composition, meaning the elements combine in a specific, unchanging ratio. Others have a variable composition, where the proportions of the components can change.

Analyzing the Options

• Brass: This is an alloy, primarily made of copper (Cu) and zinc (Zn). The proportions of copper and zinc can be adjusted, resulting in different types of brass with varying properties. Therefore, brass has a variable composition.
• Water: Chemically represented as H₂O, water is a compound. It always consists of hydrogen and oxygen atoms in a fixed ratio of 2:1.
• Hydrogen chloride: Chemically represented as HCl, this is a compound formed by the fixed combination of hydrogen and chlorine atoms in a 1:1 ratio.
• Methane: Chemically represented as CH₄, methane is a compound composed of carbon and hydrogen atoms in a fixed ratio of 1:4.

Conclusion on Composition

Based on the analysis, only brass among the given options exhibits variable composition because it is an alloy whose components can be mixed in different proportions.