A metal rod of length 10 cm and a rectangular cross-section of $1 \mathrm{cm} \mathrm{x} \frac{1}{2}\mathrm{cm}$ is connected to a battery across opposite faces. The resistance will be

As we know that, 
$\mathrm{R}=\mathrm{\rho }\left(\frac{\mathrm{l}}{\mathrm{A}}\right)$
The maximum resistance will be achieved when the value of $\frac{\mathrm{l}}{\mathrm{A}}$,  is maximum, so that ‘A’ must be minimum and it is minimum when area of cross section is 1 cm x 1/2 cm