Why is nichrome commonly used as the heating element in electric heaters?

Correct — C. A heating element must turn current into heat and survive being red-hot.

High resistivity gives it enough resistance in a short, sturdy coil, so it produces most of the circuit's heat (H = I²Rt).
A high melting point, about 1,400 °C for nichrome, keeps it from melting at working temperature.

NCERT adds that alloys do not oxidise readily at high temperatures, which is why heaters use them. Option (c).

Why the others are wrong

• (a)
  It has low resistivity and a high melting point — Low resistivity is what the copper cord needs, so it stays cool. An element made that way would need a very long, thin wire to reach the resistance a heater needs.
• (b)
  It has high resistivity and a low melting point — A low melting point suits a fuse, which NCERT describes as a wire that melts and breaks the circuit when the current is too high. A heating element must glow without melting.
• (d)
  It offers low resistivity and a low melting point — This fails on both counts: low resistivity gives little heat from a short wire at a given current, and a low melting point would let the element fail once hot.

Joule's law of heating, H = I²Rt, says a conductor carrying current I for time t produces heat in proportion to its resistance R. The heater's cord and its element carry the same current, so the part with far higher resistance, the element, gets hot.

Resistance depends on the material through resistivity (ρ), in R = ρl/A. NCERT notes that an alloy's resistivity is generally higher than that of its constituent metals.

Key facts

• Joule's law of heating: H = I²Rt.
• Resistance R = ρl/A, and the SI unit of resistivity is the ohm metre (Ω m).
• Nichrome melts at about 1,400 °C.
• NCERT: tungsten, with a melting point of 3380 °C, is used for bulb filaments, and copper and aluminium for transmission lines.

Common traps

• Picking high resistivity with a low melting point by mixing up a heating element with a fuse wire.
• Assuming good conductors make good heaters: low resistivity is why the cord stays cool while the element glows.

No directly related past PYQ was found.