The Third Law of Thermodynamics provides an absolute reference point for entropy: for a perfectly ordered crystal at 0 K, (S = 0). This is a profound consequence because it allows absolute entropies (not just entropy differences) to be calculated by integrating (C_p/T) from 0 K to the desired temperature, accounting for all phase transitions along the way. This is the basis for standard molar entropies (S^\circ) tabulated in thermodynamic tables. Option A is incorrect because the Third Law applies only to perfect crystals — substances with residual disorder (like ice with hydrogen-bond disorder) have non-zero residual entropy at 0 K. Option C is incorrect — reactions can have (\Delta S \neq 0) at absolute zero if the products and reactants have different residual entropies. Option D is the opposite of what the Third Law enables: it actually makes low-temperature entropy measurements possible and meaningful. This is an NCERT and JEE Advanced conceptual question on the Third Law. Plausibility check: standard molar entropies are always positive (or zero) for all pure substances, consistent with the Third Law providing a universal zero reference.