Chlorosis is a condition characterized by the yellowing of leaves, which is caused by a deficiency of essential nutrients in plants. The correct answer to the question is option 'D', which states that chlorosis can be caused by the deficiency of zinc, potassium, and manganese.

Zinc Deficiency:
- One of the causes of chlorosis is a deficiency of zinc in the soil. Zinc is an essential micronutrient that plays a crucial role in various plant processes, including chlorophyll synthesis.
- Chlorophyll is responsible for the green color of leaves and is vital for photosynthesis, the process by which plants convert sunlight into energy.
- When plants lack zinc, their chlorophyll synthesis is disrupted, leading to a decrease in chlorophyll levels and the appearance of yellow leaves.

Potassium Deficiency:
- Another nutrient deficiency that can result in chlorosis is potassium deficiency. Potassium is an essential macronutrient required by plants for proper growth and development.
- Potassium is involved in numerous physiological processes, including enzyme activation, osmoregulation, and protein synthesis.
- In the absence of sufficient potassium, plants are unable to carry out these processes effectively, leading to a disruption in chlorophyll synthesis and the subsequent yellowing of leaves.

Manganese Deficiency:
- The third nutrient deficiency associated with chlorosis is manganese deficiency. Manganese is a trace mineral that plays a crucial role in photosynthesis, enzyme activation, and nutrient uptake.
- In the absence of manganese, plants are unable to produce chlorophyll effectively, resulting in chlorosis and the yellowing of leaves.

In conclusion, chlorosis, characterized by yellowing leaves, can be caused by the deficiency of essential nutrients such as zinc, potassium, and manganese. These nutrients are essential for chlorophyll synthesis and other vital plant processes.