The star antares has a mass of 3.08 x 1031 kg.
how might this star be classified?

The correct answer is supergiant.  

Explanation:  

The largest stars in the universe are known as the supergiant stars. They can be thousands of times larger in comparison to the Sun and exhibits a mass of up to 100 times greater. The supergiants come in an array of temperatures and sizes, however, they are usually categorized as being either blue or red.  

The red supergiants exhibit a mass of about 8 times more than the Sun, and are usually old stars, which were once identical in size to the Sun. On the other hand, the blue supergiants are hotter in comparison to the red supergiants, however, are much smaller in size.