In the crust of the Earth, which metal is the most abundant by weight, occurring mainly in the form of oxides and silicate minerals such as bauxite and feldspars?

Introduction / Context:
This question belongs to geochemistry and general science. It asks about the most abundant metal in the crust of the Earth. Knowing which elements are most common in the crust helps in understanding mineral resources, industrial metallurgy and why certain metals are widely used in construction and manufacturing.

Given Data / Assumptions:

• We are concerned with the composition of the Earth crust, not of the whole Earth or the core.
• The options include several common metals: iron, magnesium, calcium, aluminium and copper.
• We assume average crustal composition by weight as reported in standard geology and chemistry references.
• We focus on metals, not non metals like oxygen and silicon, which are also very abundant in the crust.

Concept / Approach:
The crust of the Earth is composed primarily of oxygen and silicon, but when we look specifically at metals, aluminium stands out as the most abundant by weight. Aluminium occurs mainly in the form of silicate minerals and in bauxite ore (hydrated aluminium oxides). Iron is another abundant metal, but in the crust it is less abundant than aluminium. Therefore, although iron dominates the core of the Earth, aluminium is the most abundant metal in the crust itself.

Step-by-Step Solution:
1) Recall that oxygen and silicon are the most abundant elements in the Earth crust, forming silicate minerals.2) When considering metals only, common candidates include aluminium, iron, calcium, sodium, potassium and magnesium.3) Aluminium makes up a significant percentage of the crust by weight, often quoted around eight percent, mostly in the form of aluminosilicates and bauxite.4) Iron is also abundant but typically present in lower percentage than aluminium in the crust and is concentrated more in the core of the Earth.5) Calcium and magnesium are important constituents of rocks but are less abundant than aluminium when compared by total crustal content.6) Copper is present only in trace amounts compared with aluminium and iron.7) Therefore, among the metals listed, aluminium is the most abundant metal in the crust of the Earth.

Verification / Alternative check:
Standard tables of crustal abundance show that oxygen is first, followed by silicon, then aluminium as the third most abundant element overall and the most abundant metal. Iron usually appears slightly lower in percentage for the crust. Mining and metallurgical data also reflect the huge importance of aluminium ore deposits such as bauxite. These independent sources are consistent with the statement that aluminium is the most abundant metal in the Earth crust, confirming the correctness of the answer.

Why Other Options Are Wrong:
Iron: Very abundant and essential in geology and industry, but in the crust its abundance is lower than that of aluminium.
Magnesium: An important component of many silicate minerals, especially in the mantle, but not as abundant as aluminium in the crust.
Calcium: Significant in limestone and some silicates, but its overall crustal abundance is lower than aluminium.
Copper: Economically important but geochemically much less abundant than aluminium, existing mainly in smaller ore deposits.

Common Pitfalls:
Students sometimes confuse the composition of the crust with that of the whole Earth. Because iron is abundant in the core, they may wrongly assume iron is the most abundant metal overall. It is helpful to distinguish clearly between crust (outer layer) and core (inner region). In the crust, aluminium dominates among metals, while iron dominates in the core. Remembering that bauxite and aluminosilicate minerals are widespread in rocks helps fix aluminium as the correct answer for crustal abundance questions.

Final Answer:
The most abundant metal in the crust of the Earth is aluminium.