The trend is such that the general substances tend to show an increase in the volume levels with the rise in the temperature levels. This trend is reversed when the opposite takes place, like the substance is allowed to cool down.
You need to be aware of the term saturation state which is indicated by the points 2,3 4, and 5. It is a phenomenon where a change of phase occurs without any deviation in the level of temperature. With regards to this the pressure is also constant. From this diagram the point 2 goes on to indicate a solid state and on the other hand the state 1 can never be regarded as a saturated state as the temperature is bound to change before the melting tends to occur. It is at point 3 which is considered to be the stage of saturation because at this stage the change of phase from liquid to solid is bound to happen because of cooling.
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