Just as a good conductor is related to copper, in the same way a bad conductor is related to what?

Now, we check each options.

Option (a): Wood – A very poor conductor of electricity (insulator). It does not allow electricity to pass through unless it is wet.

Option (b): Aluminium – A good conductor, though not as good as copper. It is used in electrical wiring.

Option (c): Iron – A moderate conductor, better than many materials but not as good as copper or aluminium.

Option (d): Coal – Its conductivity varies. Pure carbon (graphite form) conducts electricity, but other forms of coal are poor conductors.

So, Wood is bad conductor.

Thus, correct option is (a).