Resistivity of a metallic conductor varies with temperature as $\rho_T = \rho_0[1 + \alpha(T - T_0)]$. The temperature coefficient of resistivity $\alpha$ has dimensions of

1. In $\rho_T = \rho_0[1 + \alpha(T-T_0)]$ the bracketed term must be dimensionless. 2. So the product $\alpha(T-T_0)$ must be dimensionless. 3. Since $(T-T_0)$ has dimension of temperature, $\alpha$ must have dimension (temperature)$^{-1}$. 4. Thus B; a dimensionless $\alpha$ (D) would make the product carry temperature units. _Source: NCERT Class 12 Physics Ch 3 "Current Electricity", p.9_