Chemistry

Question Analysis
This question involves identifying a substance with a unique phase diagram feature (negative solid-liquid boundary slope). The main focus is on recognizing the exception to the general phase diagram slope rule.

Key Concept Explanation
For most substances (e.g., CO₂, ethanol, O₂), the solid phase is denser than the liquid phase, resulting in a positive slope for the solid-liquid boundary line (increasing pressure favors the denser solid phase).
Water is the key exception: Liquid water is denser than solid ice (due to hydrogen bonding in ice creating an open lattice structure), resulting in a negative slope (increasing pressure favors the denser liquid phase, melting ice at lower temperatures).

Step-by-Step Solution
1. Recall the exception: Only water (among common substances) has a negative solid-liquid boundar...