How does the resistivity of alloys compare with those of pure metals from which they may have been formed?

$(a)$ Resistivity of iron is $10 \times 10^{-8} \; \Omega m$ and of mercury is $94 \times 10^{-8} \; \Omega m$. Which among iron and mercury is a better conductor? Give reason.
$(b)$ Resistivity of a material $A$ is in the range of $10^{10}-10^{14} \; \Omega m$ while that of $B$ is in the range of $10^{-6}-10^{-8} \; \Omega m$. Which of the two will behave as an insulator and why?

$A$ copper wire has a diameter of $0.5\, mm$ and a resistivity of $1.6 \times 10^{-8}\, \Omega \, m$. What will be the length of this wire to make its resistance $10\, \Omega$? How much does the resistance change if the diameter is doubled?

Which one of the following is true according to Ohm's law?

The $I-V$ graph for a given metallic wire at three different temperatures is shown. Which of these represents the highest temperature?

$A$ wire is $1.0 \, m$ long,$0.2 \, mm$ in diameter and has a resistance of $10 \, \Omega$. Calculate the resistivity of its material.