Change Of State

Step 1: Understanding the Concept:
The process of heating ice at all the way to steam at involves three distinct thermodynamic stages.
It involves a phase change from solid to liquid, a pure temperature increase of the liquid, and finally a phase change from liquid to gas.
Step 2: Key Formula or Approach:
During a phase change, heat is strictly supplied as latent heat ( ), and the absolute temperature remains entirely constant, leading to a horizontal line on a Temperature vs. Heat graph.
During a single-phase temperature rise, heat goes into specific heat capacity ( ), causing the temperature to rise linearly with a constant positive slope.
Step 3: Detailed Explanation:
Let's trace the correct physical sequence of the heating curve:
Stage 1: Ice at melts into liquid water at . The temperature strictly remains constant at as heat is continuously supplied. This produces a horizontal line segment starting right from the origin along the heat axis.
Stage 2: The liquid water is then heated from up to . The temperature continuously rises linearly as more heat is supplied, creating a diagonal straight line moving upward.
Stage 3: The water at begins to boil and convert entirely into steam. The temperature remains completely constant at during this entire process, forming a second horizontal line segment.
Looking strictly at the provided visual options, Graph B is the only graph that perfectly depicts this exact "horizontal-diagonal-horizontal" sequence starting from the origin.
Step 4: Final Answer:
Graph B correctly represents the exact variation of temperature with the heat supplied.