Computer Network: Collision and broadcost Domains

Basically collision domain is where the frames may collide so collisiion domain is where you have half duplex running with csma\cd . So a hub is a complete collision domain where each device connected is sharing the same bus and are in the same collision domain and also in the single broadcast domain
A broadcast domain is where a packet destined is flooded into the whole network with destination ip address of 255.255.255.255 and mac address all ones i.e, ff.ff.ff.ff.ff.ff with each device connected processing the frame whether it is of its use or not. switches and hub broadcast the frames but switches also multicasts and unicasts the frames
A switch does not share the same bus instead it has full duplex running on each port and each port is its collision domain ,so the no. of ports a switch has is the no of collision domains and a complete broadcast domain. In case you connect a hub in a port of switch it should run in half duplex and csma\cd and so is in its collision domain .
a router is a layer 3 device and is used to segment broadcast domains so depends on the topology and the no of ethernet ports .there is no concept of collision domain in a router as it is a layer 2 concept
If you have any doubt tell me now