The table lists five metals in order of reactivity. The method used to extract each metal is linked to its reactivity. Metal Reactivity Method of extraction...

This question links a metal's reactivity to how it is extracted, and reviews redox and recycling.

(a) Filling the extraction-method column by comparing each metal with carbon:

Metals above carbon (potassium, aluminium) need electrolysis; those below carbon but still reactive (zinc, iron) are reduced with carbon; gold is unreactive enough to be found uncombined.

(b) The most reactive metals are more reactive than carbon, so they cannot be extracted by carbon reduction and can only be obtained by electrolysis [1]. Electrolysis needs an electric current, which was not available until a supply of electricity was developed in the early nineteenth century [1].

(c) The more reactive a metal is, the more strongly it holds onto the oxygen in its oxide [1], so more energy is needed to remove that oxygen and the metal is harder to reduce/extract [1].

(d) Low-grade copper ores are now used because the rich, high-grade ores are running out [1], while demand and the price of copper remain high, making it economic to process ores that contain only a little copper [1].

(e) The general half-equation for reducing a metal ion \( M^{3+} \) to the metal is:

This scores [1]; the ion gains three electrons.

(f) In terms of electron transfer, reduction is the gain of electrons [1].

(g) Any two reasons recycling matters, one mark each up to [2]: it conserves limited ore/metal reserves; it saves energy compared with extracting from ore; it reduces waste sent to landfill; it reduces mining and the damage it causes; it lowers cost.