The measurement that describes the pressure of gas is d) 725 mmHg.
Pressure is a fundamental property of gases and is typically measured in units such as mmHg (millimeters of mercury), atm (atmospheres), or Pa (Pascals). In this case, 725 mmHg is a direct measurement of the pressure exerted by the gas. The other options—315 K, 1.2 g/L, 2.5 L, and 0.45 moles—represent temperature, density, volume, and amount of substance respectively, but they do not describe pressure.