In metallurgy and mineral resources, which of the following minerals is an ore of aluminium used in the extraction of this metal?

Introduction / Context:
This question relates to basic metallurgy and general knowledge of ores. Different metals are extracted from specific ores, which are naturally occurring minerals with sufficient metal content. Aluminium is an important metal used in many industries. Recognising its ores is a common exam topic in chemistry and general science.

Given Data / Assumptions:

• We are asked to identify an ore of aluminium from the given list.
• Options include galena, cryolite, cinnabar, Epsom salt and rock salt.
• We assume conventional school level knowledge of common ores.

Concept / Approach:
Aluminium is mainly extracted from bauxite, but cryolite (sodium aluminium fluoride) is also associated with aluminium and used in the electrolytic extraction process. Among the given options, cryolite is the only mineral that contains aluminium in its composition. Galena is an ore of lead, cinnabar is an ore of mercury, Epsom salt is a magnesium compound and rock salt is sodium chloride. Therefore, cryolite is the correct choice as an aluminium related ore among the listed minerals.

Step-by-Step Solution:

Verification / Alternative check:
Metallurgy textbooks list bauxite as the principal ore of aluminium and also mention cryolite as an important mineral in the Hall process, where it serves as a solvent for bauxite in the electrolytic cell. Reference lists of ores match galena with lead, cinnabar with mercury, and cryolite with aluminium electrolytic processes. Because only cryolite has a direct connection to aluminium among the options, it must be the correct answer.

Why Other Options Are Wrong:

• Galena: This is PbS and is the chief ore of lead, not aluminium.
• Cinnabar: This is HgS and is the chief ore of mercury.
• Epsom salt: This is MgSO4 dot 7H2O, used as a magnesium source and in medicine, not in aluminium extraction.
• Rock salt: This is NaCl, an ore of sodium and source of common salt.

Common Pitfalls:
Students sometimes automatically think of bauxite as the only ore of aluminium and may be confused when it is not listed among the options. In such cases, it is important to recall other aluminium related minerals and choose the one most clearly linked to aluminium, which is cryolite. Another mistake is to guess based on unfamiliar names rather than connecting minerals to their known metal contents. Regular revision of common ores and their metals helps avoid such errors.

Final Answer:
The ore of aluminium among the options given is Cryolite.