Classifying substances as elements, compounds, or mixtures

Steps:

• Classify W (ethane): compound, as it consists of carbon and hydrogen atoms chemically bonded (C₂H₆).
• Classify X (air): mixture, as it contains various gases like nitrogen and oxygen physically combined.
• Classify Y (iodine): element, as it is a pure substance of iodine atoms (I₂ in molecular form).
• Classify Z (brass): mixture, as it is an alloy of copper and zinc metals blended together.

Why D is correct:

• D accurately identifies Y as an element (pure iodine), W as a compound (molecular formula C₂H₆), and X as a mixture (gaseous blend), matching definitions of pure substances versus combinations.

Why the others are wrong:

• A misclassifies W as element (ethane is compound) and Y as compound (iodine is element).
• B misclassifies W as element (ethane is compound) and Z as compound (brass is mixture).
• C misclassifies the row by assigning mixture to Z instead of X (air is the gaseous mixture here).

Final answer: D