Final answer:
The SI unit of temperature is the kelvin (K), making option b) 273 K the correct one among the choices given for expressing temperature in SI units.
Step-by-step explanation:
The option that gives an object's temperature in International System of Units (SI units) is b) 273 K. The SI unit of temperature is the kelvin, represented by the symbol K. It is an absolute temperature scale with its starting point at absolute zero, which is 0 K. This is equivalent to -273.15°C, the theoretically lowest possible temperature. The Celsius and Fahrenheit scales, which are used in various parts of the world for everyday temperature measurements, are not considered SI units. The Celsius scale places its zero point at the freezing point of water, while the Fahrenheit scale places its zero well above the freezing point of water at the temperature at which a mixture of salt and ice melts.
To convert temperatures from Celsius to Kelvin, you can add 273.15 to the Celsius temperature, as in TK = Tc + 273.15. Hence, 0°C corresponds to 273.15 K, and 273 K is slightly below the freezing point of water.