Which of the following offers non-ohmic resistance?

The correct answer is Option (4) → Diode

A conductor is ohmic when its I–V graph is a straight line through the origin. Its resistance then does not depend on the size or the direction of the applied voltage.

Option (1) Carbon resistor — Incorrect. A resistor is made to have a fixed resistance. At a steady temperature, its current is proportional to the voltage, so it obeys Ohm’s law.

Option (2) Copper wire — Incorrect. Copper is a metal. At a steady temperature, its free electrons drift with a speed proportional to the field. So its current is proportional to the voltage.

Option (3) Nichrome wire — Incorrect. Nichrome is a metal alloy with a steady resistivity, so its I–V graph is also a straight line.

Option (4) Diode — Correct. The I–V graph of a diode is curved. Reversing the voltage also does not give a current of the same size in the opposite direction. So its resistance depends on V.

NCERT (2026-27):
Points to Ponder – “… A resistor obeys Ohm’s law while a diode does not. … The Ohm’s law asserts that the plot of I versus V is linear i.e., R is independent of V.”