According to the NCERT text (Exercise 3.5), the relationship between resistance and temperature is given by $R_2 = R_1 [1 + \alpha (T_2 - T_1)]$. Rearranging for the temperature coefficient $\alpha$: $\alpha = \frac{R_2 - R_1}{R_1(T_2 - T_1)}$. Given: $R_1 = 2.1 \ \Omega$ at $T_1 = 27.5^\circ\text{C}$ $R_2 = 2.7 \ \Omega$ at $T_2 = 100^\circ\text{C}$ Substituting the values: $\alpha = \frac{2.7 - 2.1}{2.1 (100 - 27.5)} = \frac{0.6}{2.1 \times 72.5} = \frac{0.6}{152.25} \approx 0.0039 \ ^\circ\text{C}^{-1}$ , .