Which one of the following is a compound?

Solution

1. Glass
• Glass is a non-crystalline mixture of silica and other materials. It is not a compound because its composition is not fixed.
2. Water Gas
• Water gas is a mixture of carbon monoxide (CO) and hydrogen (H ₂ ), not a compound. It is used as a fuel but doesn't have a fixed chemical formula as a single compound.
3. CNG (Compressed Natural Gas)
• CNG is also a mixture, primarily of methane (CH ₄ ) with small amounts of other gases. It is not a compound.
4. Plaster of Paris (POP)
• Plaster of Paris is CaSO4 ⋅ 1/2H2O, a true chemical compound with a definite composition.