Which of the following graphs represents the variation of resistivity ( $\rho$ ) with temperature $(T)$ for copper?

Three copper wires of lengths and cross-sectional areas are $(l, A)$,$(2l, A/2)$,and $(l/2, 2A)$. Resistance is minimum in

$A$ tapered bar of length $L$ and end diameters $D_1$ and $D_2$ is made of a material of electrical resistivity $\rho$. The electrical resistance of the bar is

Two wires of equal length and equal diameter and having resistivities $\rho_1$ and $\rho_2$ are connected in series. The equivalent resistivity of the combination is . . . . . . .

The resistivity of alloys is $\rho_{\text{alloy}}$ and the resistivity of constituent metals is $\rho_{\text{metal}}$. Then,usually:

$A$ cylindrical wire $P$ has resistance $10 \ \Omega$. $A$ second wire $Q$ has length and diameter half that of $P$. If the material of both the wires is same,then the resistance of wire $Q$ is (in $\Omega$)