Question

what do these two changes have in common? filtering air to remove dust and pollen sanding a piece of wood select all that apply. both are changes of state. both are caused by heating. both are chemical changes. both are only physical changes.

Explanation:

1. Analyze "filtering air to remove dust and pollen": This is a physical process where dust/pollen is separated from air, no new substance is formed, and it's not a change of state (air remains gas, dust/pollen are solids) nor caused by heating.
2. Analyze "sanding a piece of wood": This is a physical process where wood surface is smoothed (shape/size change), no new substance is formed, not a change of state (wood remains solid) nor caused by heating.
3. Evaluate options:

• "Both are changes of state": Incorrect, as neither involves state (solid/liquid/gas) change.
• "Both are caused by heating": Incorrect, as neither process requires heating.
• "Both are chemical changes": Incorrect, as no new substances are formed (chemical change needs new substance).
• "Both are only physical changes": Correct, as both involve physical alterations (separation, shape change) without new substances.

Answer:

D. Both are only physical changes