Which of the following has a negative temperature coefficient of resistance?

$A$ metal rod of length $10 \ cm$ and a rectangular cross-section of $1 \ cm \times 0.5 \ cm$ is connected to a battery across opposite faces. The resistance will be . . . . . . .

$A$ and $B$ are two square plates of the same metal and same thickness,but the length of $B$ is twice that of $A$. The ratio of the resistances of $A$ and $B$ is

$A$ conductor has resistance values of $2.71 \ \Omega$ and $3.70 \ \Omega$ at $10^{\circ}C$ and $100^{\circ}C$ respectively. The temperature at which the resistance is $3.26 \ \Omega$ is .......... $^{\circ}C$.

At room temperature $(27.0^{\circ} C)$,the resistance of a heating element is $100\; \Omega$. What is the temperature (in $^{\circ} C$) of the element if the resistance is found to be $117\; \Omega$,given that the temperature coefficient of the material of the resistor is $1.70 \times 10^{-4}\; ^{\circ} C^{-1}$?

Two conductors have the same resistances at $0^{\circ} C$ but their temperature coefficients of resistance are $\alpha_1$ and $\alpha_2$. The respective temperature coefficients for their series and parallel combinations are :