The water quality of a pond was analysed and its BOD was found to be 4. The pond has

BOD measures the amount of dissolved oxygen required by aerobic microorganisms to break down the organic matter present in a given water sample. It serves as a direct indicator of organic water pollution:

• High BOD: Indicates a large amount of organic waste, which consumes significant dissolved oxygen, leaving less for aquatic life (high pollution).
• Low BOD: Indicates very little organic waste or debris, meaning the dissolved oxygen remains abundant and stable.

Standard Water Quality Classification (NCERT Guidelines):

According to environmental chemistry standards, water quality is classified based on its BOD value (measured in ppm or mg/L):

• $$\text{BOD} < 5\text{ ppm}$$: Classified as very clean water.
• $$\text{BOD} \ge 17\text{ ppm}$$: Classified as highly polluted water.

Since the analyzed pond water has a BOD value of 4 (which is less than 5), it falls squarely into the category of unpolluted, healthy water.

Note on the shared web page: The automated green checkmark on the reference page incorrectly labels it as "Highly polluted water." This is factually wrong; a low BOD value of 4 represents clean, unpolluted water.

Conclusion:

A BOD value of 4 indicates minimal organic waste, designating the pond as having clean water.

Answer: Option C — Very clean water