We can see here that the star that is the hottest is: Star D.
A star is a celestial object primarily composed of hydrogen and helium that generates energy through nuclear fusion in its core. It emits light and heat due to the energy produced by the fusion reactions occurring at its core.
The hottest stars, such as those belonging to spectral types O and B, have high temperatures and emit a significant amount of energy (high luminosity). These stars are blue or bluish-white in color and are among the most luminous stars in the universe.