Which of the following metals is the most abundant metal in the Earth crust by percentage composition?

Introduction / Context:
This question tests knowledge of geochemistry and Earth science, specifically the relative abundance of metals in the Earth crust. While oxygen and silicon are the most abundant elements overall in the crust, among metals one particular metal dominates. Learners are expected to know which metal occurs in the highest proportion in crustal rocks and therefore plays a major role in geology and mineral resources.

Given Data / Assumptions:

• The focus is on the Earth crust, not the whole Earth or the core.
• The options are magnesium, iron, copper, and aluminium.
• We consider percentage by weight of metal elements in the crust.

Concept / Approach:
The composition of the Earth crust is dominated by oxygen and silicon, forming silicate minerals. Among metals, aluminium and iron are both very common. Copper and magnesium are present but not in the highest percentages. Standard data show that aluminium is the most abundant metal in the crust, followed by iron, calcium, sodium, potassium, and magnesium in varying amounts. The approach is to recall this approximate ordering and choose the metal that comes first among the options.

Step-by-Step Solution:
Step 1: Remember that aluminium occurs mainly in minerals such as feldspars, mica, and bauxite, and is widely distributed in crustal rocks. Step 2: Recall that iron is also abundant but is less abundant than aluminium in the crust as a whole, although it is very important in the core. Step 3: Copper occurs in ore bodies and is economically important but is much less abundant in terms of total crustal composition. Step 4: Magnesium is more abundant than copper but still not as abundant as aluminium in the crust. Step 5: Therefore, among the listed metals, aluminium is the most abundant metal in the Earth crust.

Verification / Alternative check:
Geology and chemistry references often provide approximate percentages: oxygen around almost half by weight, silicon around a quarter, aluminium about 8 percent, iron around 5 percent, and other metals less. These figures confirm that aluminium is the leading metal in crustal abundance. Iron is extremely abundant in the core but the question asks specifically about the crust, which makes aluminium the correct choice among the given options.

Why Other Options Are Wrong:

• Magnesium: Present in many silicate minerals but not as abundant as aluminium in the crust.
• Iron: Very important and abundant but still occurs in a smaller percentage than aluminium when only the crust is considered.
• Copper: Much less abundant overall, though economically significant because of its conductivity and industrial uses.

Common Pitfalls:
A common error is to confuse abundance in the whole Earth with abundance in the crust. Because iron dominates the core, some learners incorrectly choose iron. Others may think in terms of economic importance, leading them to guess copper. To avoid these mistakes, always note that the question mentions the Earth crust specifically and remember that aluminium is the most abundant metal in that outermost layer.

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