BOD (Biochemical Oxygen Demand) is a measure of the amount of oxygen consumed by microorganisms in the breakdown of organic matter.
A BOD value of 0-5 indicates very clean water, as there is little organic matter to decompose.
A BOD of 6-15 indicates moderately polluted water.
A BOD higher than 15 suggests highly polluted water.
Since the BOD is 4, it indicates very clean water.
Thus, the correct answer is: (3) Very clean water.
What will be the equilibrium constant of the given reaction carried out in a \(5 \,L\) vessel and having equilibrium amounts of \(A_2\) and \(A\) as \(0.5\) mole and \(2 \times 10^{-6}\) mole respectively?
The reaction : \(A_2 \rightleftharpoons 2A\)

Cobalt chloride when dissolved in water forms pink colored complex $X$ which has octahedral geometry. This solution on treating with cone $HCl$ forms deep blue complex, $\underline{Y}$ which has a $\underline{Z}$ geometry $X, Y$ and $Z$, respectively, are
What will be the equilibrium constant of the given reaction carried out in a \(5 \,L\) vessel and having equilibrium amounts of \(A_2\) and \(A\) as \(0.5\) mole and \(2 \times 10^{-6}\) mole respectively?
The reaction : \(A_2 \rightleftharpoons 2A\)
The following are the major sources of Water Pollution: