The dissolved oxygen level in natural unpolluted waters at normal temperature is found to be of the order of
a) 1 mg/litre
b) 10 mg/litre
c) 100 mg/litre
d) 1000 mg/litre
The dissolved oxygen level in natural unpolluted waters at normal temperature is found to be of the order of
a) 1 mg/litre
b) 10 mg/litre
c) 100 mg/litre
d) 1000 mg/litre
