The graph depicts the temperature curves for two substances labeled as substance X and Y.
Why does the temperature remain constant as heat is added to each substance in the regions labeled A to B, C to D, and A' to B', and C' to D'?
Based on the curve for either substance X or substance Y and using what you know about the particulate nature of matter, and the relationship between temperature and potential or kinetic energy, describe why adding heat leads to the step-wise change in temperature depicted in the graphs.

The graph depicts the temperature curves for two substances labeled as substance X and Y Why does the temperature remain constant as heat is added to each subst class=