Brass is an alloy made up of :

An alloy is a substance formed by fusing two or more metals (or a metal with a non-metal) to produce material properties -- strength, corrosion resistance, colour, or workability -- that differ from those of the individual pure metals. Each standard alloy has a specific, named metal combination: for example, copper and tin give one well-known alloy, copper and zinc give another, and lead and tin give a third.

Brass is, by definition, the alloy formed from copper and zinc. Depending on the intended use, the zinc content typically ranges from about 5% to 40%, with the remainder copper; a higher zinc share increases strength but reduces ductility, while a higher copper share deepens the golden-yellow colour. This copper-zinc combination is why brass is widely chosen for musical instruments, decorative fittings, and plumbing components -- it is both corrosion-resistant and easy to machine.

Checking the composition against each offered pairing:

• Copper and tin is the composition of bronze, a harder and more wear-resistant alloy traditionally used for statues, bells, and bearings -- a different alloy from brass.

• Gold, iron and zinc is not a standard industrial alloy; iron has very limited solubility in molten gold, so the three metals do not combine into a stable, well-defined alloy.

• Lead and tin is the composition of solder, valued for its low melting point in joining applications, and is unrelated to the copper-zinc composition of brass.

Therefore, brass is the alloy made of copper and zinc.