For existence of aquatic life in water, the dissolved oxygen content in it, should not be less than ______________ ppm?

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Smog is ______________________?

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Coal washing waste water containing about 3% suspended solids (comprising of clay, slate, stone etc.) is treated for solid particles removal ?

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Which of the following is the common pollutant emitted from metallurgical smelters, thermal power plant and cement plants ?

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Noise level inside a jet airliner in normal flight is about ______________ decibels?

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