Will my motherboard be compatible with an i7 6700k?

Solution
it mean it won't fit

go to asrock website for the mobo and check the cpu supported list
http://www.asrock.com/mb/AMD/990FX%20Extreme9/
Like rgd1101 said, it won't fit.

Cpu's and sockets are designed to fit properly with one another. The 990FX is an amd motherboard and the i7 6700k is an intel cpu. The only compatible sockets with an i7 6700k are lga 1151, in otherwords h110, h170, b150, z170. If planning to overclock you'll need a z170 chipset for it.