Explanation:

The Rankine cycle is a thermodynamic cycle that is commonly used in power plants to generate electricity. It consists of four main components: a pump, a boiler, a turbine, and a condenser. The cycle operates by converting heat energy into mechanical work, which is then used to drive a generator.

Internal irreversibility refers to the energy losses that occur within the system due to various factors. These losses result in a decrease in the overall efficiency of the cycle. The internal irreversibilities in a Rankine cycle are caused by the following factors:

1. Fluid friction:
Fluid friction occurs when the working fluid passes through pipes, valves, and other components of the system. This friction leads to a loss of energy in the form of heat, resulting in a decrease in the overall efficiency of the cycle.

2. Throttling:
Throttling refers to the process of reducing the pressure of the working fluid by expanding it through a valve or a nozzle. This process is necessary in the Rankine cycle to decrease the pressure of the working fluid before it enters the turbine. However, throttling is an irreversible process and leads to a loss of energy in the form of heat.

3. Mixing of fluids:
In some cases, the working fluid may mix with other fluids during the cycle. For example, in a regenerative Rankine cycle, the working fluid may mix with the feedwater before entering the boiler. This mixing of fluids results in a loss of energy and reduces the overall efficiency of the cycle.

However, the temperature difference between the combustion gases and the working fluid does not cause internal irreversibilities in the Rankine cycle. In fact, this temperature difference is essential for the operation of the cycle. The combustion gases provide heat to the working fluid, which is then used to drive the turbine and generate power. Therefore, option B is incorrect.

In conclusion, the internal irreversibilities in a Rankine cycle are primarily caused by fluid friction, throttling, and the mixing of fluids. The temperature difference between the combustion gases and the working fluid is not a cause of internal irreversibility in the cycle.