Understanding the Question:
The question asks which of four numbered climatic zones is categorized as hot and dry.
Key Concept:
Drug stability testing conditions are set by climatic zone, where each zone number is tied to a fixed combination of temperature and relative humidity representative of that region's climate.
Checking Each Option:
Zone-I is the temperate zone, tested near 21 degrees C and 45% relative humidity, too mild to be called hot and dry.
Zone-II is the subtropical or Mediterranean zone, tested near 25 degrees C and 60% relative humidity, warm but not dry.
Zone-IV is hot and humid, tested near 30 degrees C with high relative humidity around 65 to 75%, hot but wet rather than dry.
Zone-III is fixed as the hot and dry zone, tested near 30 degrees C and only about 35% relative humidity, matching high heat with low moisture.
Final Answer:
Zone-III is the climatic zone categorized as hot and dry.