Conductors → allow electricity to flow, e.g. metals like Gold, Silver.
These are good conductors of electricity.
Insulators → block electricity, e.g. non-metals like Diamond.
Diamond is a bad conductor of electricity.
Graphite → is a special case, it's a non-metal but → conducts electricity.
So, it's not the answer we're looking for.
Answer: Diamond, as it's a bad conductor of electricity → doesn't allow electricity to flow.
Option 1: Diamond is the correct answer.