Question

Water has Maximum density at temperature

• A. $273\text{ }^0\text{K}$
• B. $277\text{ }^0\text{K}$
• C. $289\text{ }^0\text{K}$
• D. $298\text{ }^0\text{K}$

Hint:

The anomalous expansion of water is critical for aquatic ecosystems in cold climates.
Since water is densest at $4\text{ }^\circ\text{C}$ ($277\text{ K}$), the heavier $4\text{ }^\circ\text{C}$ water sinks to the bottom of lakes, allowing ice to form at the surface ($0\text{ }^\circ\text{C}$) and protecting aquatic life below.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Water exhibits an anomalous expansion behavior between $0\text{ }^\circ\text{C}$ and $4\text{ }^\circ\text{C}$.
Unlike most liquids that expand upon heating, water contracts as its temperature rises from $0\text{ }^\circ\text{C}$ to $4\text{ }^\circ\text{C}$, reaching its maximum density at approximately $4\text{ }^\circ\text{C}$.

Step 2: Key Formula or Approach:
To convert the temperature from the Celsius scale ($t$) to the Kelvin scale ($T$):
\[ T\text{ (K)} = t(^\circ\text{C}) + 273.15 \]

Step 3: Detailed Explanation:
The hydrogen bonds in ice form a highly structured, open hexagonal crystalline lattice with significant void spaces.
As ice melts at $0\text{ }^\circ\text{C}$, this rigid cage-like structure partially collapses, allowing water molecules to pack more closely together.
From $0\text{ }^\circ\text{C}$ to $4\text{ }^\circ\text{C}$, the breaking of these residual hydrogen-bonded clusters continues to dominate, increasing the packing density despite thermal agitation.
At $4\text{ }^\circ\text{C}$, the density of pure water reaches its maximum value of $1.0000\text{ g/cm}^3$ (or $1000\text{ kg/m}^3$).
Above $4\text{ }^\circ\text{C}$, normal thermal expansion due to increased molecular motion dominates, causing the density to decrease.
Converting the temperature of maximum density to Kelvin:
\[ T = 4 + 273.15 = 277.15\text{ K} \]
This value is closest to $277\text{ K}$.

Step 4: Final Answer:
Water has its maximum density at a temperature of $277\text{ }^0\text{K}$.
Therefore, the correct option is (B).