Classifying substances as elements, compounds, or mixtures Steps:

• Elements consist of one type of atom only (e.g., graphite is pure carbon, iron is pure Fe).
• Compounds contain two or more elements chemically bonded (e.g., methane is CH₄, water is H₂O).
• Mixtures involve substances physically combined without bonding (e.g., air is mixed gases, brass is copper-zinc alloy).
• Check each option's pairs against these definitions for full accuracy.

Why B is correct:

• B is not; water is a compound (H₂O, two elements bonded), not an element, and graphite is an element (pure C), not a compound.

Why the others are wrong:

• A: Copper is an element (pure Cu), not a mixture.
• C: Methane is a compound (CH₄), not an element.
• D: Water and methane are compounds, not elements; air is a mixture, not a compound.

Final answer: None