On which factors does the resistivity of a conducting wire depend?

Nichrome is used to make the element of an electric heater. Why?

The filament of an electric bulb is made of tungsten. Why?

The $V-I$ graphs for two resistors of the same material and the same radii with lengths $L_{1}$ and $L_{2}$ are shown below. If $L_{1} > L_{2}$, state with reason, which of these graphs represents voltage-current change for $L_{1}$?

What are the conditions under which $Ohm's$ law is not obeyed?

Find out the following in the electric circuit given in the figure:
$(a)$ Effective resistance of two $8\, \Omega$ resistors in the combination.
$(b)$ Current flowing through $4\, \Omega$ resistor.
$(c)$ Potential difference across $4\, \Omega$ resistor.
$(d)$ Power dissipated in $4\, \Omega$ resistor.
$(e)$ Difference in ammeter readings,if any.