What size chain for 200gs FC-M202?
Narrow means whatever was derailleur chain at the time, as opposed to wider singlespeed chain. The actual chain type is determined by the cassette and is very probably 7-speed.

The inch designations listed on Wikipedia are not commonly used except to distinguish between 1/8" singlespeed chain and narrower derailleur chains that are all lumped under 3/32" and distinguished by number of speeds in cassette. Note that on Wikipedia 7.1mm and 7.3mm both become 9/32".