Which of the following has a variable composition?

Correct option is A

The correct answer is (A) Brass

Explanation:
• In chemistry, substances are broadly classified into pure substances (elements and compounds) and mixtures.
• Compounds have a fixed, definite chemical composition. Mixtures, on the other hand, consist of two or more substances physically combined, meaning their ratio or composition can vary.
• Brass is an alloy made primarily of copper and zinc. Because it is a solid mixture (alloy), the percentage of copper and zinc can be altered to produce different types of brass with varying mechanical and electrical properties. Therefore, it has a variable composition.

Information Booster:
• Alloys: Alloys are considered homogeneous mixtures of metals (or a metal and a non-metal). For example, steel is an alloy of iron and carbon.
• Proust's Law of Definite Proportions: This fundamental law states that a chemical compound always contains exactly the same proportion of elements by mass. Mixtures do not obey this law.

Additional Knowledge:
• Option B (Water): Water (H2O) is a chemical compound. It always contains hydrogen and oxygen in a fixed 2:1 atomic ratio (or 1:8 mass ratio).
• Option C (Hydrogen chloride): HCl is a compound with a fixed 1:1 atomic ratio of hydrogen to chlorine.
• Option D (Methane): Methane (CH4) is a compound with a fixed 1:4 atomic ratio of carbon to hydrogen.