Assuming that "RADIUS" in the title of this post is a typo: 100 meters is the range without any obstacles, i. e. outdoor. Indoor you will never reach 100 meters. The coverage depends on the antenna and the environment. There are walls, different materials, furniture, people, etc. You cannot predict the coverage. So a very important step in wireless design is a site survey, before and after the installation. If you do not want or cannot do a site survey, you have to determine the best transmit power experimental. The Meraki dasboard can help with the integrated tools (Wireless -> RF Spectrum). Here you can see the channel utilization and the interfering APs.
Yes, the coverage of 5 GHz is lower than of 2.4 GHz. With a given medium (air) the attenuation is four times higher with two times higher frequency.