Question

1. where on the graph are phase changes taking place?

(options: 2, 3, 1, 5, 4)

Explanation:

In a heating - time graph for phase changes, during phase changes (like melting or boiling), the temperature remains constant while heat is being added. On the graph, the flat (horizontal) segments represent these constant - temperature periods where phase changes occur. Segment 3 and segment 4 are the horizontal parts of the graph, so phase changes take place at these segments.

Answer:

3, 4