On a two-component solid-liquid phase diagram, an isopleth indicates which of the following?

1. A region where the composition of the system is constant
2. An area above which only the liquid phase exists
3. A region where the pressure is constant
4. An area below which only the solid phase exists

The diagram given below represents pressure vs composition phase diagram (at constant T).


The point at which only liquid exist is:

The reading of pressure gauge at which only liquid phase exists is:

The above diagram is known as phase diagram. The phase diagram for a substance is shown in the figure where $T$ is temperature in Kelvin and $P$ is pressure in atmospheres. For example if a substance at a particular temperature and pressure lies in gas area , the substance exists only as a gas.
However, if the temperature-pressure pairing is on the line segment between gas and liquid, the substance exists as both a gas and a liquid.. If $T>0$ and $P>0$, which of the following systems of inequalities would describe the temperature and pressure ranges in which this substance exists only as a liquid?