A wire has a resistance of 2.1 Ω at 25°C and a resistance of 2.8 Ω at 100°C. The temperature coefficient of the resistance is:

$4.4×10^{-3} °C^{-1}$

The correct answer is Option (3) → $4.4×10^{-3} °C^{-1}$

The temperature coceficient of resistance ($α$) is,

$R_T=R_0(1+α(t-t_0))$

$⇒α=\frac{R_t-R_0}{R_0(t-t_0)}$

$⇒α=\frac{2.8-2.1}{2.1(100-25)}=\frac{0.7}{2.1×75}$

$=\frac{0.7}{157.5}≃0.00444$ per °C