ANS:A - 0

The statement "entropy at 273 K equals 0" is generally true for an ideal crystalline substance at absolute zero temperature (0 K), but it is important to understand the context and limitations of this statement. Entropy (S) is a thermodynamic property that quantifies the degree of randomness or disorder in a system. At absolute zero temperature (0 K), an ideal crystalline substance is in its lowest possible energy state, with all molecular motion ceasing. In this state, the system is in perfect order, and there are no positional or energetic degrees of freedom available to molecules. For an ideal crystalline substance at absolute zero temperature, the entropy is usually defined as zero because there is no randomness or disorder present in the system. However, it's crucial to note that this concept applies strictly to idealized, perfectly ordered crystalline structures, which may not perfectly represent real-world substances. In reality, substances may have residual entropy at absolute zero due to factors such as zero-point energy (the lowest possible energy state allowed by quantum mechanics) and quantum mechanical effects. Additionally, real substances may not exhibit perfectly ordered crystalline structures at all temperatures, and their entropy at 273 K (0°C) will depend on various factors such as molecular structure, phase (solid, liquid, or gas), and external conditions. Therefore, while the statement "entropy at 273 K equals 0" holds true for an idealized scenario of an ideal crystalline substance at absolute zero temperature, it may not necessarily apply to real-world substances and situations.