Bitcoin / Crypto and exchanges!

[Bitcoin]

Bitcoin / Crypto and exchanges!

When we buy/ sell bitcoin through some exchange say "Koinex in Indian context", what is the process i.e. actually followed ?
1. Does exchange communicate to node(s) in the bitcoin blockchain thru my public address on my behalf or
2. My browser directly communicates with node in blockchain which then broadcast it across bitcoin blockchain or
3. Exchange itself is a node in the network and to which i am communicating and it is broadcasting my transaction in the network

Source: Bitcoin / Crypto and exchanges!