Introduction:
The state of a substance refers to its physical form, such as solid, liquid, or gas. Pressure and temperature are two important factors that determine the state of a substance.

Pressure:
Pressure refers to the amount of force exerted on a given area. When the pressure of a substance increases, its particles become more closely packed together, resulting in a change of state. For example, when water is subjected to high pressure, it can turn into ice.

Temperature:
Temperature refers to the degree of hotness or coldness of a substance. When the temperature of a substance changes, its particles can either move faster or slower, resulting in a change of state. For example, when water is heated, it can turn into steam.

Phase Diagram:
A phase diagram is a graph that shows the relationship between pressure, temperature, and the state of a substance. It is used to determine the conditions under which a substance will exist in a particular state. The phase diagram of water, for example, shows that at normal atmospheric pressure, water exists as a liquid between 0°C and 100°C, and as a solid below 0°C and as a gas above 100°C.

Conclusion:
In conclusion, pressure and temperature are two important factors that determine the state of a substance. The phase diagram provides a useful tool for understanding the relationship between pressure, temperature, and the state of a substance. Understanding these concepts is essential for many applications, including the design of industrial processes, the study of materials science, and the understanding of weather patterns.

A change in temperature or pressure will result in the change of state of the substance. 

for example ice, if we change the temperature it will started melting resulting change of state from solid to liquid and if increase temperature then it will evaporates resulting change from liquid to vapour (gas).
A solid can be converted into liquid and then to gas by decreasing the pressure and increasing the temperature. Every state of matter of any substance is stable at a corresponding pressure and temperature. Thus, temperature and pressure determines the state of a substance.

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