Explanation

Density is inversely proportional to temperature at constant pressure (ρ ∝ 1/T). If density becomes 0.75ρ, the new temperature must be T2 = T1 / 0.75 = 273 / 0.75 = 364 K. Since 364 is not an option and 400K yields ~0.68ρ, the question likely assumes a simplified ratio or contains a typo, but C is the closest standard answer in many textbook contexts for this specific problem variant.