c
For no deflection $\frac{0.8}{1}=\frac{R}{3}$
$\Rightarrow \mathrm{R}=2.4 \mathrm{~m} \Omega$
Temperature fall in $10 \mathrm{~s}=20^{\circ} \mathrm{C}$
$\Delta \mathrm{R}=\mathrm{R} \alpha \Delta \mathrm{t}$
$\alpha=\frac{\Delta \mathrm{R}}{\mathrm{R} \Delta \mathrm{t}}=\frac{-0.6}{3 \times 20}$
$=-10^{-2} \mathrm{C}^{-1}$