Please answer these questions

$9.$ What is IEEE $802.$x$?$

$10.$ Explain what is the difference between persistent, non$-$persistent and p$-$persistent CSMA.

$11.$ What is the purpose of the SOF $($start of frame$)$ field in the Ethernet frame?

$12.$ What is the purpose of virtual LANs? Why not use just the physical LAN topology?