Answer: Vacuum.
- A Water
- B Steel
- C Vacuum
- D Air
Correct answer: C. Vacuum
Explanation: Sound is a mechanical wave and requires a medium to propagate. It cannot travel through vacuum.
A standing wave forms from two identical waves travelling in opposite directions and interfering; nodes (always zero displacement) and antinodes (maximum displacement) stay fixed in place, unlike a travelling wave where the whole pattern moves.
Concept context
Wave types, superposition, standing waves, Doppler effect, and sound intensity.