Video narration
Look at Question 1: a wire has resistance R ohm. It is melted and then stretched to n times its original length. What is the new resistance? Use the resistance formula: R = ρL/A, where ρ is resistivity, L is length, and A is cross‑sectional area. Since it’s the same material, ρ stays the same. Melting and remaking the wire means the amount of material is unchanged, so volume stays constant: V = LA. If the new length is L′ = nL, then the new area must be A′ = V/L′ = LA/(nL) = A/n. Now compute the new resistance: R′ = ρL′/A′ = ρ(nL)/(A/n) = ρL/A · n^2 = R·n^2. So the new resistance is n^2 R, which matches option B.