Step 1: Understanding the Concept:
Electrical resistance is a measure of the opposition to current flow in an electrical circuit.
Step 2: Detailed Explanation:
The Standard International (S.I.) unit of resistance is named after the German physicist Georg Simon Ohm.
It is represented by the Greek letter Omega (\(\Omega\)).
Step 3: Final Answer:
The S.I. unit is the Ohm.