BOD values (in ppm) for clean water (A) and polluted water (B) are expected respectively
(a) A 50,

Q: What exactly does BOD measure?

BOD measures the amount of dissolved oxygen consumed by microorganisms while they decompose organic matter in water. It's an indirect measure of organic pollution.

Q: Why is the BOD of clean water less than 5 ppm?

Clean water contains very little organic waste. Therefore, there isn't much for bacteria to break down, so they consume very little oxygen, keeping the BOD below 5 ppm.

Q: What happens to aquatic life if BOD is very high?

A high BOD means bacteria are consuming most of the dissolved oxygen in the water. This leaves very little oxygen for fish and other aquatic organisms, which can lead to their suffocation and death.

Q: Is BOD the same as Dissolved Oxygen (DO)?

No, they are opposites in a way. DO is the actual amount of oxygen present in the water, while BOD is the amount of oxygen *demanded* or consumed by bacteria. High BOD usually leads to low DO.

Q: Can BOD be zero?

In perfectly pure, sterile water with absolutely zero organic matter and no microorganisms, the BOD would theoretically be zero. However, in natural environments, water always has a small, non-zero BOD.

Question

BOD values (in ppm) for clean water ($A$) and polluted water ($B$) are expected respectively Options: (A) $A > 50, B < 27$ (B) $A > 25, B < 17$ (C) $A < 5, B > 17$ (D) $A > 15, B > 47$

Sigma Percentile · Accepted Answer

### The Story of Biochemical Oxygen Demand (BOD) Imagine a beautiful, clear lake. The water is pristine, and fish are swimming happily. Now, imagine a stagnant pond filled with sewage and decaying leaves. What is the fundamental chemical difference between these two bodies of water? The answer lies in a crucial environmental parameter called **Biochemical Oxygen Demand**, or **BOD**. ### What exactly is BOD? BOD is a measure of the amount of dissolved oxygen that aerobic microorganisms (like bacteria) need to decompose the organic matter present in a water sample. Think of it as the "appetite" of the bacteria in the water. If a water body has a lot of organic waste (like sewage, dead plants, or agricultural runoff), there will be a massive feast for the bacteria. As they multiply and eat this waste, they consume a huge amount of dissolved oxygen from the water. This high demand for oxygen means the water has a **high BOD**. Conversely, if the water is clean and pure, there is very little food for the bacteria. They won't consume much oxygen, resulting in a **low BOD**. ### The Standard Values Environmental scientists have established standard benchmarks to classify water quality based on BOD values (measured in parts per million, or ppm): 1. **Clean Water:** For water to be considered clean and safe, its BOD value must be very low. Specifically, the BOD of clean water is **less than $5 ext{ ppm}$**. 2. **Highly Polluted Water:** When a water body is heavily contaminated with organic waste, the oxygen demand skyrockets. Water is classified as highly polluted when its BOD value is **greater than $17 ext{ ppm}$**. ### Solving the Problem In our question, we are given two types of water samples: - Sample $A$: Clean water - Sample $B$: Polluted water Based on the standard benchmarks we just discussed, we can immediately deduce the expected BOD values: - For clean water $A$, the BOD must be less than $5 ext{ ppm}$. So, **$A < 5$**. - For polluted water $B$, the BOD must be greater than $17 ext{ ppm}$. So, **$B > 17$**. Looking at the given options, the only one that perfectly aligns with these scientific standards is option (c): $A < 5, B > 17$. Understanding BOD is not just about memorizing numbers; it's about understanding the delicate balance of aquatic ecosystems. When BOD gets too high, the dissolved oxygen drops so low that fish and other aquatic life can suffocate and die, leading to dead zones. That's why monitoring BOD is essential for environmental protection!

Animated Solution for Chemistry - Environmental Chemistry: BOD values (in ppm) for clean water ( $A$ ) and polluted water ( $B$ ) are expected respectively

Select Answer:

Visualized Solution

\text{Understanding BOD}

\text{BOD of Clean Water}

\text{BOD of Polluted Water}

\text{Evaluating Options}

The Sigma Insight: Water and Soil Pollution

The Story of Biochemical Oxygen Demand (BOD)

What exactly is BOD?

The Standard Values

Solving the Problem

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Animated Solution for Chemistry - Environmental Chemistry: .math-text-wrapper .katex { font-size: 1.05em !important; } .math-text-wrapper .katex-display { margin: 1rem 0 !important; } BOD values (in ppm) for clean water (A) and polluted water (B) are expected respectively