Given below are two statements.
Statement I The value of the parameter "Biochemical Oxygen Demand (B

Q: Why does high BOD mean low dissolved oxygen?

BOD measures the oxygen consumed by bacteria to decompose organic waste. If there's a lot of waste, bacteria multiply and consume more oxygen, leaving less dissolved oxygen for fish and other aquatic life.

Q: Can BOD be exactly zero?

In a perfectly pure water sample with absolutely no organic matter, the BOD would theoretically be zero. However, in natural water bodies, there is always some minimal organic matter, so BOD is rarely exactly zero.

Q: Is 6.5 ppm BOD considered safe for drinking?

No. Clean drinking water should have a BOD of less than 5 ppm (ideally 1-2 ppm). A BOD of 6.5 ppm indicates moderate organic pollution and would require treatment before consumption.

Q: What causes BOD to increase in a river?

Discharge of untreated sewage, agricultural runoff containing fertilizers, and industrial effluents rich in organic matter are the primary causes of increased BOD in rivers.

Q: How is BOD measured in the lab?

BOD is typically measured by taking a water sample, measuring its initial dissolved oxygen, incubating it in the dark at 20°C for 5 days, and then measuring the final dissolved oxygen. The difference gives the BOD5 value.

Question

Given below are two statements.
Statement I The value of the parameter "Biochemical Oxygen Demand (BOD)" is important for survival of aquatic life.
Statement II The optimum value of BOD is 6.5 ppm.
In the light of the above statements, choose the most appropriate answer from the options given below.

Options:

(A) Statement I is false but statement II is true.

(B) Both statements are true.

(C) Statement I is true but statement II is false.

(D) Both statements are false.

Sigma Percentile · Accepted Answer

### The Breath of the River

Imagine a serene, crystal-clear river. Beneath its surface, a delicate balance of life thrives. Fish, plants, and microscopic organisms all depend on one invisible, life-sustaining element: **Dissolved Oxygen (DO)**.

But what happens when organic waste—like sewage or agricultural runoff—enters this pristine ecosystem? This is where our crucial parameter, **Biochemical Oxygen Demand (BOD)**, comes into play.

BOD is essentially a measure of how much oxygen the aerobic bacteria will consume as they feast on the organic waste. If there is a massive feast (high waste), the bacteria multiply rapidly and consume a massive amount of oxygen.

This leaves the fish gasping for air. Therefore, a high BOD directly translates to dangerously low Dissolved Oxygen.

### Decoding the Statements

Let's look at **Statement I**: "The value of the parameter BOD is important for survival of aquatic life."

Given our understanding, this statement is an absolute truth. Monitoring BOD is like checking the pulse of a water body. If the BOD is too high, the aquatic ecosystem is suffocating. It is a critical indicator of water health.

Now, let's analyze **Statement II**: "The optimum value of BOD is $6.5 	ext{ ppm}$."

To judge this, we need to know the standard benchmarks. For truly clean and healthy water, the BOD should be extremely low, typically **less than $5 	ext{ ppm}$**.

On the extreme end, highly polluted water—the kind that resembles an open sewer—has a BOD of **$17 	ext{ ppm}$ or more**.

### The Verdict

So, where does $6.5 	ext{ ppm}$ fit in? It sits above the clean water threshold. A BOD of $6.5 	ext{ ppm}$ indicates that the water is moderately polluted.

The "optimum" value for the survival of aquatic life should be as close to zero as possible, definitely below $5 	ext{ ppm}$. Therefore, claiming that $6.5 	ext{ ppm}$ is the optimum value is factually incorrect.

**Statement I is True**, and **Statement II is False**. This leads us directly to our final answer.

Select Answer:

Visualized Solution

$B O D$

$B O D vs D O$

$Evaluating Statement I$

$BOD of Clean Water$

$BOD of Polluted Water$

$Evaluating Statement II$

$Final Conclusion$

The Sigma Insight: Water and Soil Pollution

The Breath of the River

Decoding the Statements

The Verdict

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