In metallurgical chemistry, which of the following is the most important ore of aluminium?

Introduction / Context:
This question belongs to the topic of metallurgy and ores. An ore is a naturally occurring mineral from which a metal can be profitably extracted. Aluminium is a widely used metal and its main ore is a standard fact in chemistry curricula. The question asks you to identify the most important ore of aluminium from the list provided.

Given Data / Assumptions:

• The metal of interest is aluminium.
• You are given four minerals: calamine, monazite, magnetite and bauxite.
• Only one of these is the principal commercial source of aluminium.
• Standard names and uses of common ores are assumed.

Concept / Approach:
Aluminium is extracted mainly from bauxite, a hydrated aluminium oxide mineral. Bauxite typically contains aluminum hydroxides along with impurities such as iron oxides and silica. The Bayer process is used to purify bauxite and obtain alumina, which is then reduced by electrolysis in the Hall Heroult process to give aluminium metal. Calamine is an ore of zinc, magnetite is an ore of iron and monazite is a phosphate mineral that is an important source of rare earth elements and thorium. Therefore, only bauxite is correctly associated with aluminium extraction.

Step-by-Step Solution:
Step 1: Recall the standard list of important ores. For aluminium, the primary ore is bauxite. Step 2: Bauxite consists largely of hydrated aluminium oxides, such as gibbsite and boehmite, along with impurities. Step 3: In the Bayer process, bauxite is digested in sodium hydroxide to dissolve alumina and separate impurities. Step 4: The alumina obtained is then electrolysed in molten cryolite to produce pure aluminium metal. Step 5: Calamine is a zinc ore (zinc carbonate or related minerals), not an aluminium ore. Step 6: Magnetite is an iron oxide used as an iron ore. Step 7: Monazite sands are sources of thorium and rare earths, not aluminium.

Verification / Alternative check:
Look at typical tables of ores and metals found in textbooks. Against aluminium you will almost always see bauxite listed as the chief ore, sometimes along with cryolite in specific contexts, though cryolite is mostly used as a flux rather than a principal ore. In contrast, zinc is paired with ores like zinc blende and calamine, iron is paired with hematite, magnetite and siderite and thorium with monazite. This cross checking confirms that bauxite is the only appropriate ore listed for aluminium.

Why Other Options Are Wrong:
Calamine is primarily zinc carbonate and is an ore of zinc, not aluminium. Magnetite is iron oxide Fe3O4 and an important ore of iron, often used in the blast furnace process. Monazite is a phosphate mineral rich in rare earth metals and thorium, used in nuclear fuel and related applications. None of these minerals serves as a major source of aluminium. Therefore, they cannot be the correct answer in a question about the principal ore of aluminium.

Common Pitfalls:
Students sometimes remember the names of ores but forget which metal they belong to, leading to confusion between bauxite, magnetite and others. Another mistake is to assume that because aluminium is light, its ore might be a light coloured mineral like some carbonates, but this is not a reliable guide. To avoid this, memorise a simple mapping: bauxite for aluminium, hematite and magnetite for iron, zinc blende and calamine for zinc, and monazite for thorium. This mapping simplifies many ore related questions.

Final Answer:
The most important ore of aluminium is bauxite.