Which one of the following statements is correct?

Correct — A, Alloys are mixtures. School chemistry defines an alloy as a homogeneous mixture of two or more metals, or of a metal and a non-metal, and each word of that definition rules out one of the other options. A mixture has no fixed composition, and brass is made across a wide band of copper-to-zinc ratios while remaining brass, which no compound could do. Nothing new is formed in a fixed proportion by mass, and the constituents keep their own chemical identity — they are simply melted together and allowed to solidify as a uniform solid. What does change is the physical behaviour: hardness, melting point, electrical resistance and corrosion resistance all shift, which is the entire reason for alloying in the first place.

• (b)Alloys are compounds. — A compound has a fixed composition by mass and a definite formula. Steel can carry anywhere from a fraction of a per cent of carbon to nearly two per cent and is still steel, and the components can be recovered without chemical decomposition.
• (c)Alloys are always made up of metals. — Steel is the standing counterexample — iron alloyed with carbon, a non-metal. The definition itself allows a metal with a non-metal, so 'always' is what breaks this option.
• (d)All alloys contain carbon as one of their components. — Carbon belongs to the steels, not to alloys in general. Brass is copper and zinc, bronze is copper and tin, solder is lead and tin, and an amalgam is mercury with another metal — none of them contains carbon.

An alloy is a homogeneous mixture obtained by melting two or more metals together, or a metal with a non-metal, and letting the melt solidify. Because it is a mixture, the proportions can be varied continuously and the components keep their chemical character; because it is homogeneous, the result looks and behaves like a single material rather than a blend of visible grains. The reason for making one is almost always a physical property — pure iron is soft, pure gold too soft to hold a setting, pure copper too weak for a bearing.

The four options here are a neat map of the ways a student can half-know this topic. Someone who remembers only that alloying produces a new material with new properties will choose 'compounds'. Someone who remembers the word 'metal' in the definition and not the rest will choose 'always made up of metals'. Someone whose only worked example was steel will choose the carbon option. Learning one non-carbon alloy and one metal-plus-non-metal alloy is enough to close all three doors: brass for the first, steel for the second.

• An alloy is a homogeneous mixture of two or more metals, or of a metal and a non-metal.
• Steel is iron with a small proportion of carbon, which is why an alloy need not be entirely metallic.
• Brass is copper and zinc; bronze is copper and tin; solder is lead and tin; an amalgam is mercury with another metal.
• Alloys have no fixed composition by mass and no chemical formula, unlike compounds.
• Alloying raises hardness and resistance to corrosion and usually lowers the melting point of the mixture below that of the higher-melting constituent — the property that makes solder useful.
• The electrical conductivity of an alloy is lower than that of its parent metal, which is why heating elements use nichrome rather than pure nickel.

• Treating an alloy as a compound because it has properties neither parent metal shows.
• Assuming every alloy is metal-only and forgetting steel.
• Generalising carbon from the steels to all alloys.

Framed as a single-correct-statement item where three options are over-general — 'compounds', 'always', 'all' — and the right one is the plain textbook definition.

• practice — not a real PYQ

  Which one of the following alloys does not contain copper?

  • (a)Brass
  • (b)Bronze
  • (c)Solder
  • (d)German silver

  Answer(c) Solder — an alloy of lead and tin. Brass is copper and zinc, bronze copper and tin, and German silver copper with zinc and nickel.

• practice — not a real PYQ

  An alloy differs from a compound in that

  • (a)it always has a fixed composition by mass
  • (b)its components can be present in varying proportions
  • (c)it can be separated only by chemical means
  • (d)it is always harder than every one of its constituents

  Answer(b) its components can be present in varying proportions — the absence of a fixed composition is what makes an alloy a mixture.