Introduction:
The use of hydrogen in an Electrolux refrigeration system is aimed at affecting the rate of evaporation of the liquid ammonia passing through the evaporator. The correct option in this case is option 'C', which states that hydrogen is used to increase the rate of evaporation. Let's understand why this is the correct answer.

Explanation:
- In an Electrolux refrigeration system, ammonia is the working fluid that undergoes a phase change from liquid to vapor and vice versa in order to transfer heat and cool the refrigerated space.
- The evaporator is the component where the liquid ammonia evaporates and absorbs heat from the surroundings, causing the refrigerated space to cool down.
- The rate of evaporation, or the amount of liquid ammonia that vaporizes per unit time, is an important factor in determining the cooling capacity of the system.
- By introducing hydrogen into the system, the rate of evaporation of liquid ammonia is increased.
- This is because hydrogen has a lower molecular weight compared to ammonia, and it diffuses more rapidly.
- The presence of hydrogen increases the rate at which ammonia molecules escape from the liquid phase and enter the vapor phase, thus increasing the evaporation rate.
- This leads to more efficient heat transfer and faster cooling of the refrigerated space.
- The use of hydrogen in the Electrolux refrigeration system helps to enhance the overall performance and efficiency of the system.
- It should be noted that the use of hydrogen in refrigeration systems requires careful design and control to ensure safety and prevent any potential hazards associated with hydrogen.

Conclusion:
In summary, hydrogen is used in the Electrolux refrigeration system to increase the rate of evaporation of the liquid ammonia passing through the evaporator. This helps to improve the cooling capacity and efficiency of the system.