How to determine the root port

The root port will be determined based on the algorithm below.
1. Lowest port cost
2. Lowest value of the forwarding switch's ID
3. Lowest port priority
4. Lowest internal port number

RootGuard

RootGuard prevents a port to be a ND (non designated) port. So the port should always be designated. If the port receive a better BPDU, the port will become root-inconsistent state and the port will be blocking

LoopGuard

LoopGuard need to be enabled on Root Ports and Alternate Ports. When the port is not receiving BPDU, then the port will become a Loop-Inconsistent blocking state.

Looks simple, but unfortunately the sample answer of a question I got didn't match with my answer. Need to dig more about this.