V-I graph for a platinum wire at temperatures $T_1$ and $T_2$ is shown in the given figure. The temperature difference $(T_2-T_1)$ is proportional to:

$\cot 2θ$

The correct answer is Option (4) → $\cot 2θ$

for a metal like platinum, the resistance is,

$R_T=R_0(1+α(T-T_0))$

and,

The temperature difference is proportional to the change in the slopes of the V-I graphs.

$T_2-T_1∝\tan(90-2θ)$

$∝\cot 2θ$