Answer: B. Temperature
Explanation:
The temperature of the star such as Sun is measured. Using this measurement, its peak wavelength and energy can be determined.
For determination of wavelength, Wien's displacement law is used. This law states that, the sun like body emits all kinds of wavelengths and thus is nearly a black body.
For black body, the peak wavelength emitted is inversely proportional to the temperature of the body. From the wavelength, energy can be calculated.
Temperature is the property which is primarily responsible for determining the type of electromagnetic energy and peak wavelength emitted by star.