Animated Solution for Chemistry - Environmental Chemistry: Water filled in two glasses $A$ and $B$ have BOD values of $10$ and $20$, respectively. The correct statement regarding them, is

Have you ever wondered how scientists determine if a lake or a river is heavily polluted just by taking a small water sample? They don't count the bacteria one by one; instead, they measure how much the bacteria are "breathing." This brings us to a fascinating and crucial concept in environmental chemistry: Biochemical Oxygen Demand (BOD).

Imagine a glass of water taken from a local pond. It looks clear, but it's teeming with microscopic life and organic waste (like dead leaves or agricultural runoff). Bacteria in the water naturally break down this organic waste, but to do so, they need oxygen.

Biochemical Oxygen Demand (BOD) is defined as the amount of dissolved oxygen required by aerobic bacteria to decompose the organic matter present in a certain volume of a water sample.

Think of it as a proxy for pollution. If there is a massive amount of organic waste in the water, the bacteria will go into a feeding frenzy, consuming a huge amount of oxygen. Therefore, a higher BOD value directly indicates a higher level of organic pollution.

To make sense of BOD values, environmental scientists have established standard benchmarks:

- Clean Water: For water to be considered clean and suitable for drinking, its BOD value must be strictly less than $5\text{ ppm}$ (parts per million). - Highly Polluted Water: If the BOD value reaches $17\text{ ppm}$ or higher, the water is classified as highly polluted. At this level, the oxygen is depleted so rapidly that aquatic life, like fish, can suffocate and die.

In our problem, we are given two glasses of water: - Glass $A$ has a BOD of $10\text{ ppm}$. - Glass $B$ has a BOD of $20\text{ ppm}$.

Let's evaluate Glass $A$ first. Since its BOD is $10\text{ ppm}$, it is well above the safe drinking limit of $5\text{ ppm}$. This means Glass $A$ is polluted and definitely not suitable for drinking.

Now, let's look at Glass $B$. Its BOD is a staggering $20\text{ ppm}$. Not only is this above the safe limit, but it also crosses the $17\text{ ppm}$ threshold, placing it in the category of highly polluted water.

When we compare the two, the logic is straightforward. Since the BOD of Glass $B$ ($20\text{ ppm}$) is greater than the BOD of Glass $A$ ($10\text{ ppm}$), Glass $B$ contains significantly more organic waste. The bacteria in Glass $B$ are demanding twice as much oxygen as those in Glass $A$.

Therefore, we can confidently conclude that Glass $B$ is more polluted than Glass $A$.

This simple yet powerful metric allows us to quantify pollution and take necessary steps to protect our vital water resources!