The correct answer is: C. 20°C
Sewage is a mixture of wastewater from homes and businesses, as well as industrial waste. It is typically treated in a sewage treatment plant before being released back into the environment. The average temperature of sewage in India is 20°C. This is because the average temperature in India is 25°C, and sewage is heated by the sun and by the heat generated by the decomposition of organic matter.
Option A: 10°C is too cold for sewage. Sewage is a mixture of wastewater and organic matter, and both of these things decompose at a faster rate when they are warmer. This means that if the temperature of sewage is too low, it will not decompose properly and could become a health hazard.
Option B: 15°C is a bit too cold for sewage, but it is still within the range of temperatures where sewage can decompose properly. However, if the temperature of sewage is too low, it will take longer to decompose and could become a health hazard.
Option C: 20°C is the ideal temperature for sewage. This is because it is warm enough for sewage to decompose properly, but not so warm that it becomes a health hazard.
Option D: 25°C is too warm for sewage. Sewage is a mixture of wastewater and organic matter, and both of these things decompose at a faster rate when they are warmer. This means that if the temperature of sewage is too high, it will decompose too quickly and could become a health hazard.