The water having more dissolved O2 is
(a) boiling water
(b) water at 80°C
(c) polluted water
(d) wat

Q: Why is the dissolution of a gas in a liquid always exothermic?

When a gas dissolves, its molecules go from a highly disordered, high-energy state (gas phase) to a more ordered, restricted state (liquid phase). This loss of kinetic energy and entropy is released into the surroundings as heat, making $\Delta H$ negative.

Q: Does pressure affect the solubility of oxygen in water?

Yes, absolutely! According to Henry's Law, the solubility of a gas is directly proportional to its partial pressure above the liquid. However, in this specific question, we assume the atmospheric pressure is constant across all options.

Q: Why does polluted water have less dissolved oxygen?

Polluted water often contains dissolved salts and organic matter. Dissolved salts attract water molecules, leaving fewer water molecules available to trap oxygen (the salting-out effect). Furthermore, bacteria breaking down organic waste actively consume the dissolved oxygen.

Q: What happens to fish in shallow ponds during a hot summer?

During a hot summer, the water temperature rises significantly. As we learned, this decreases the solubility of oxygen. The water becomes oxygen-depleted, which can lead to fish suffocating—a phenomenon often called a 'summer fish kill'.

Q: Is there any gas whose solubility increases with temperature?

It is extremely rare. For standard non-reactive gases like $O_2$, $N_2$, and $CO_2$, solubility always decreases with temperature. Exceptions exist only in complex cases where the gas reacts endothermically with the solvent, but for standard JEE syllabus, assume gas solubility decreases with heating.

Question

The water having more dissolved $O_2$ is

Options:

(A) boiling water

(B) water at $80^\circ 	ext{C}$

(C) polluted water

(D) water at $4^\circ 	ext{C}$

Sigma Percentile · Accepted Answer

### The Secret of Aquatic Life: Gas Solubility

Have you ever wondered why aquatic life, like fish and vibrant coral reefs, thrives so beautifully in cold ocean currents rather than in warm, tropical surface waters? The answer lies not in biology, but in the fundamental physical chemistry of how gases dissolve in liquids.

### The Thermodynamics of Dissolution

Imagine a gas molecule, say oxygen ($O_2$), zipping around freely in the air with high kinetic energy. For this gas to dissolve into water, it must be captured by the water molecules. When the gas enters the liquid phase, it loses a significant amount of its kinetic energy. Where does this energy go? It is released into the surroundings as heat.

Because heat is released, the dissolution of a gas in a liquid is strictly an **exothermic process**. We can represent this chemical equilibrium as:

$	ext{Gas} + 	ext{Solvent} ightleftharpoons 	ext{Solution} + 	ext{Heat}$

### Enter Le Chatelier's Principle

Now, let's bring in Le Chatelier's Principle, which states that a system at equilibrium will try to counteract any change imposed upon it. If we heat the water (increasing the temperature), we are essentially adding heat to the product side of our equilibrium equation.

To relieve this added thermal stress, the system shifts backward. The solution breaks apart, and the dissolved gas is forced back out into the atmosphere. Therefore, **as temperature increases, the solubility of a gas in a liquid decreases**.

### Evaluating the Scenarios

Let's apply this master concept to the options provided in our problem:

1. **Boiling Water ($\approx 100^\circ 	ext{C}$):** At this extreme temperature, the thermal energy is so high that almost all dissolved gases are driven out. This is why boiling water tastes 'flat'—it has lost its dissolved oxygen.
2. **Water at $80^\circ 	ext{C}$:** While not boiling, this is still very hot. The solubility of oxygen here is extremely low.
3. **Polluted Water:** Pollution introduces dissolved solids and organic waste. Dissolved solids reduce the space available for gas molecules (a phenomenon known as the 'salting-out' effect), and organic waste often contains bacteria that actively consume whatever little oxygen is left.
4. **Water at $4^\circ 	ext{C}$:** This is the coldest option. According to our thermodynamic logic, the lowest temperature will favor the forward exothermic reaction, allowing the maximum amount of oxygen to remain dissolved.

### The Final Verdict

Water at **$4^\circ 	ext{C}$** holds the highest concentration of dissolved $O_2$. This beautiful quirk of chemistry is the very reason why cold, deep ocean waters are the lifeblood of our planet's marine ecosystems.

Animated Solution for Chemistry - Solutions: The water having more dissolved $O_{2}$ is

Select Answer:

Visualized Solution

$Thermodynamics of Dissolution$

$Le Chatelier’s Principle$

$Analyzing the Options$

$Conclusion$

The Sigma Insight: Henry's Law and Raoult's Law

The Secret of Aquatic Life

The Thermodynamics of Dissolution

Enter Le Chatelier's Principle

Evaluating the Scenarios

The Final Verdict

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Animated Solution for Chemistry - Solutions: .math-text-wrapper .katex { font-size: 1.05em !important; } .math-text-wrapper .katex-display { margin: 1rem 0 !important; } The water having more dissolved O2​ is