Chemistry

Question Analysis
This question tests the student's understanding of the critical point on a phase diagram and its significance.

Key Concept Explanation
The critical point on a phase diagram is the highest temperature and pressure at which a substance can exist as both a liquid and a gas in equilibrium. Beyond this point, the substance exists as a supercritical fluid.

Step-by-step Solution
1. Identify the key points on a phase diagram.
2. Understand the definition of the critical point.
3. Option A: It is the point where the solid, liquid, and gas phases coexist - incorrect, this is the triple point.
4. Option B: It is the highest temperature and pressure at which a substance can exist as a liquid and gas in equilibrium - correct, this...