Which of the compounds is composed of Al, Si, O and H?

Analyze the question: We need the compound whose composition includes aluminium (Al), silicon (Si), oxygen (O) and hydrogen (H).

Explain the concept: Look at the chemical formula of each option and check which elements it contains.

Solution:

• A. Epsom salt: MgSO₄·7H₂O. It contains Mg, S, O and H. There is no Al or Si, so it is not the answer.
• B. Limestone: CaCO₃. It contains Ca, C and O only, so it is not the answer.
• C. Clay: Clay is a hydrated aluminosilicate. A common example is kaolinite, Al₂Si₂O₅(OH)₄, or Al₂O₃·2SiO₂·2H₂O. It contains Al, Si, O and H, so it matches.
• D. Urea: CO(NH₂)₂. It contains C, O, N and H, so it is not the answer.

Only clay contains all four elements: aluminium, silicon, oxygen and hydrogen.

Answer: C. Clay

Exam tip: Remember these pairings:

• Clay → aluminosilicate (Al, Si, O, H)
• Limestone/marble/chalk → CaCO₃
• Epsom salt → MgSO₄·7H₂O (the question writes "Epson", but it means "Epsom")
• Urea → a nitrogen fertilizer, CO(NH₂)₂

If you see Al and Si together in a question, think of clay or other aluminosilicates, such as feldspar and mica.