What is meant by $1$ ohm resistance?

The $SI$ unit of resistivity of the material is $......$

$(a)$ 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?

The potential difference across the terminals of a cell is $1.5 \ V$. If it is connected with a resistance of $30 \ \Omega$,calculate the current flowing through the circuit. (in $A$)

Electrical resistivity of a given metallic wire depends upon

$V-I$ graphs for two wires $A$ and $B$ are shown in the figure. If both the wires are made of the same material and are of equal thickness,which of the two is of more length? Give justification for your answer.