The climatic zone where coffee plantations are primarily found in Karnataka:

Arid Zone
Semi-Arid Zone
Tropical Humid Zone
Coastal Zone

The correct answer is C) Tropical Humid Zone.

Coffee plantations are primarily found in the Tropical Humid Zone of Karnataka. This zone is characterized by high rainfall, warm temperatures, and a long growing season. The ideal climate for coffee cultivation is between 1,500 and 2,000 meters above sea level, with an average temperature of 20-25 degrees Celsius and an annual rainfall of 1,500-2,000 mm. The Tropical Humid Zone of Karnataka meets these requirements, making it ideal for coffee cultivation.

The Arid Zone is characterized by low rainfall, hot temperatures, and a short growing season. The Semi-Arid Zone is characterized by moderate rainfall, warm temperatures, and a medium growing season. The Coastal Zone is characterized by high rainfall, warm temperatures, and a long growing season. However, the Coastal Zone is too humid for coffee cultivation, as coffee plants are susceptible to diseases in humid conditions.

Therefore, the correct answer is C) Tropical Humid Zone.