In the graph, a sample of water is heated from 40 degrees Celsius to 100 degrees Celsius. Which statement correctly describes the curve?
A) QR- liquid only
RS- phase change liquid-gas
ST- gas only
B) QR- liquid only
RS- phase change liquid-solid
ST- solid only
C) QR- solid only
RS- phase change solid-liquid
ST- liquid only
D) QR- phase change solid-liquid
RS- liquid only
ST- phase change liquid-gas

Given that the temperature is at 40 degrees the water is at its liquid state while at the plateau stage ( RS ) the liquid water changes its state to gaseous. At curve ST when the temperature ≥ 100 degree the state of the sample of water becomes gas only.

Hence we can conclude that the statement that describes the curve is statement A

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