Compressions in longitudinal waves occur where the displacement-position graph has a negative slope

Steps:

• Identify the graph: displacement (vertical) vs. distance along wave (horizontal), positive rightward.
• Recall definition: compression where particles bunch up, i.e., slope du/dy < 0 (displacement decreases with position).
• Examine slopes at labelled points: A (positive slope), B (negative slope), C (zero slope), D (positive slope).
• Select point with negative slope as compression.

Why B is correct:

• At B, negative slope means particles ahead have less positive (or more negative) displacement, bunching them closer per wave mechanics.

Why the others are wrong:

• A: Positive slope indicates rarefaction (particles spread out).
• C: Zero slope indicates equilibrium (no compression or rarefaction).
• D: Positive slope indicates rarefaction (particles spread out).

Final answer: B