What is a dark area of gas on the sun that is cooler than surrounding gases called?

A dark area of gas on the sun that is cooler than the surrounding gases is known as a sunspot. Sunspots form in areas where the sun's magnetic field inhibits convection, which, in turn, lowers the temperature of the gas in that region compared to the hotter, surrounding areas. The temperatures of sunspots are typically around 3,000 to 4,000 degrees Celsius, while the sunny surface of the sun (photosphere) is around 5,500 degrees Celsius. This temperature difference is why sunspots appear dark against the bright backdrop of the sun’s surface.

Sunspots can often be seen in groups and are indicative of magnetic activity within the sun. Their formation and visibility are critical for understanding solar cycles and the sun's overall magnetic behavior. Other options, such as solar flares, chromosphere, or solar prominences, refer to different solar phenomena and do not represent the cooler areas of gas described in the question.