The degree of freedom refers to the number of variables that can be independently varied in a system without changing the number of phases or overall composition of the system. In the case of pure liquid benzene, the degree of freedom is 2.

Below are the reasons why the correct answer is option 'B':

Phase Rule:
The number of degrees of freedom in a system can be determined using the phase rule equation: F = C - P + 2, where F is the degrees of freedom, C is the number of components, and P is the number of phases.

Components:
In the case of pure liquid benzene, there is only one component, which is benzene itself. Therefore, C = 1.

Phases:
Since we are considering pure liquid benzene, there is only one phase present, which is the liquid phase. Therefore, P = 1.

Calculation:
Using the phase rule equation, we can calculate the degrees of freedom:

F = C - P + 2
F = 1 - 1 + 2
F = 2

This means that in a system of pure liquid benzene, we have two degrees of freedom.

Explanation:
The degrees of freedom represent the number of variables that can be independently changed. In the case of pure liquid benzene, there are two variables that can be independently varied without changing the number of phases or overall composition of the system.

These variables could be, for example, temperature and pressure. By changing the temperature and pressure, we can observe how the properties of the liquid benzene change, such as its density or viscosity. However, it is important to note that these changes will not alter the fact that the system remains a pure liquid benzene.

In summary, pure liquid benzene has two degrees of freedom, allowing for independent variation of two variables without changing the number of phases or overall composition of the system.