In the combustion of a hydrocarbon, which of the following products are always formed?

• A. C and H2O
• B. CO and H2
• C. CO2 and O2
• D. CO2 and H2O

Answer: (D)

Verified step by step guidance

1. Step 1: Understand the combustion reaction of a hydrocarbon, which generally involves a hydrocarbon (composed of carbon and hydrogen) reacting with oxygen (O\_2) from the air.
2. Step 2: Write the general combustion reaction for a hydrocarbon \( C_xH_y \): \[ C_xH_y + O_2 \rightarrow \text{products} \]
3. Step 3: Recognize that complete combustion of a hydrocarbon produces carbon dioxide (CO\_2) and water (H\_2O) as products because carbon atoms combine with oxygen to form CO\_2, and hydrogen atoms combine with oxygen to form H\_2O.
4. Step 4: Note that incomplete combustion can produce carbon monoxide (CO) or even elemental carbon (C), but these are not always formed; they depend on oxygen availability.
5. Step 5: Conclude that the products always formed in complete combustion of hydrocarbons are carbon dioxide (CO\_2) and water (H\_2O), which matches the correct answer.