Brass is an alloy of which two metals?

The correct answer is B, Au, that is gold. Malleability is the property of being beaten into thin sheets and ductility the property of being drawn into wires, and gold possesses both to the highest degree of any metal: a single gram can be beaten into a sheet of about one square metre and drawn into a wire of great length, which is why gold leaf and gold wire have been made for centuries. Option A is wrong because sodium is so soft that it can be cut with a knife and is reactive enough to be stored under kerosene, so it cannot be drawn into a usable wire. Option C is wrong because cerium, a lanthanide used in lighter flints and alloys, is brittle and not valued for either property. Option D is wrong because mercury is the only metal that is liquid at room temperature, and a liquid can be neither beaten into sheets nor drawn into wires.

The correct answer is B, lead. Galena is lead sulphide, with the formula PbS, and is the principal ore from which lead is extracted; being a sulphide, it is concentrated by froth flotation and then roasted to the oxide before reduction. Option A is wrong because the ores of zinc are zinc blende, which is the sulphide ZnS, and calamine, which is the carbonate ZnCO3. Option C is wrong because tin comes from cassiterite or tin stone, the oxide SnO2, and is refined by liquation. Option D is wrong because mercury comes from cinnabar, the sulphide HgS, and is refined by distillation since it boils at a low temperature. The habit to build is to read the ending of the name: most sulphides of this group end in blende, pyrites, galena or cinnabar, while carbonates end in ite and are calcined rather than roasted.

The correct answer is B, sulphide ores. In froth flotation the powdered ore is agitated with water, a frothing agent such as pine oil and a collector. Sulphide particles are preferentially wetted by oil and are carried up with the froth, while the earthy gangue is wetted by water and settles at the bottom, so zinc blende and copper pyrites are concentrated this way. Option A is wrong because oxide ores are usually heavier than the gangue and are concentrated by hydraulic washing, as with haematite and tin stone. Option C is wrong because carbonate ores are not oil-wetted and are normally concentrated by washing before calcination. Option D is wrong because halide ores such as rock salt are soluble in water and are handled by dissolution and crystallisation. A depressant such as sodium cyanide can hold one sulphide back while another floats.

The correct answer is B. Calcination is the heating of an ore in the absence or a limited supply of air and below its melting point, so that water of hydration and carbon dioxide are driven off; it is therefore the step used for carbonate ores such as calamine and for hydrated ores such as bauxite. Option A is wrong because heating in a plentiful supply of air is roasting, which is applied to sulphide ores such as zinc blende, where sulphur escapes as sulphur dioxide. Option C is wrong because adding a reducing agent such as coke is the separate step of smelting or reduction, which comes after calcination or roasting. Option D is wrong because both calcination and roasting are deliberately carried out below the melting point; melting the ore is the business of smelting. Both steps share one aim, to obtain the oxide, which is the form easiest to reduce.

The correct answer is B. Zone refining rests on the fact that impurities are more soluble in a molten metal than in the same metal when solid. A narrow molten zone is created with a mobile heater and moved slowly along the rod, so the impurities travel with the melt and collect at one end, which is then cut off; the method gives the ultra-pure silicon, germanium and gallium used in semiconductors. Option A is wrong because a lower boiling point is the basis of refining by distillation, used for zinc, mercury and cadmium. Option C is wrong because the formation of a volatile carbonyl is the basis of the Mond process for nickel, where nickel carbonyl decomposes on stronger heating. Option D is wrong because oxidation into a porous cupel describes cupellation, used to separate silver from lead.