Yes, the B250 motherboard supports the I5-8400 processor. The B250 motherboard uses the LGA1151 interface, and the I5-8400 is also an eighth-generation Intel processor based on the LGA1151 interface, so it is fully compatible. In addition, the B250 motherboard is equipped with an eighth-generation processor compatibility BIOS, ensuring that the I5-8400 processor can be installed and used normally. In short, you can safely choose a B250 motherboard with an I5-8400 processor without worrying about compatibility issues.