Question

The second-most abundant oxide in the Earth's crust is

• A. Al$_2$O$_3$
• B. SiO$_2$
• C. CaO
• D. Na$_2$O

Hint:

Silicon dioxide (SiO$_2$) is a major component of the Earth's crust, forming minerals like quartz and contributing to the crust's composition.

Answer 1

The Correct Option is A

Analysis of Oxide Abundance

The eight most abundant elements in the Earth's crust are almost entirely found as oxides. Their typical abundance (by mass percent of the oxide form) is:

Silicon dioxide ($\text{SiO}_2$): $\approx 59\%$

Aluminum oxide ($\text{Al}_2\text{O}_3$): $\approx 15\%$

Iron(III) oxide ($\text{Fe}_2\text{O}_3$) / Iron(II) oxide ($\text{FeO}$): $\approx 8-10\%$ combined

Magnesium oxide ($\text{MgO}$): $\approx 4\%$

Calcium oxide ($\text{CaO}$): $\approx 4\%$

Sodium oxide ($\text{Na}_2\text{O}$): $\approx 3\%$

Potassium oxide ($\text{K}_2\text{O}$): $\approx 2.5\%$

Titanium dioxide ($\text{TiO}_2$): $\approx 1\%$

Conclusion

The most abundant oxide is $\text{SiO}_2$ (Option B).

The second-most abundant oxide is $\text{Al}_2\text{O}_3$ (Aluminum oxide).

This corresponds to Option (A).