Fundamental electrical units: identify the SI unit used to measure resistance in circuits.

Introduction / Context:
Correct use of SI units prevents confusion and ensures accurate communication in engineering. Resistance quantifies how much a component opposes current flow when a voltage is applied across it. The SI unit for resistance is central to Ohm’s law and circuit calculations.

Given Data / Assumptions:

• We use the SI (International System of Units).
• Electrical quantities: voltage (V), current (A), resistance (Ω), power (W).
• Ohm’s law relates these quantities directly.

Concept / Approach:
Ohm’s law states V = I * R. Rearranging gives R = V / I. The derived SI unit of resistance is volt per ampere. This unit is given the special name “ohm,” symbol Ω. It is distinct from volt (potential), ampere (current), and watt (power).

Step-by-Step Solution:
Recall Ohm’s law: R = V / I.Identify SI base/derived units: V for volt, A for ampere, Ω for ohm, W for watt.Therefore, resistance is measured in ohms (Ω).

Verification / Alternative check:
Dimensional check: 1 Ω = 1 V / 1 A. Power relation P = V * I = I^2 * R = V^2 / R further confirms consistency of units.

Why Other Options Are Wrong:
Volt: measures electric potential difference, not resistance.Ampere: measures current, not resistance.Watt: measures power, not resistance.None of the above: incorrect since “ohm” is correct.

Common Pitfalls:
Interchanging symbols (Ω vs W vs V vs A); forgetting that resistance is a scalar property independent of frequency in ideal resistors.

Final Answer:
ohm