The lines are a representation of the substance existing in the specified phase. Thus, option B is correct.
The phase diagram of a reaction has been the representation of the phase or state of the compound that has been present at specified temperature and pressure.
The change in temperature and pressure results in the change in the phase of compounds. The phase diagram has been represented with the change of temperature and pressure at which the specified phase existed.
The phase has been differentiated from each other with the lines. Thus, the lines are a representation of the substance existing in the specified phase. Thus, option B is correct.
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