Step 1: Recall the band picture.
In a solid, electrons live in a filled valence band and an empty conduction band, with an energy gap between them. The size of this gap decides if the material conducts.
Step 2: Look at conductors.
In metals the two bands overlap or the conduction band is partly filled. So there is no real gap, and current flows easily.
Step 3: Look at semiconductors.
Here the gap is small (less than about $3$ eV). At room temperature a few electrons can jump across, giving some conduction.
Step 4: Look at insulators.
Insulators have a very large gap (often $6$ eV or more). This big gap is the key feature.
Step 5: See what the big gap does.
Because the gap is so wide, ordinary heat energy cannot push electrons across it. So electrons stay stuck in the valence band.
Step 6: State the conduction band condition.
Since no electrons cross over, the conduction band stays empty.
Step 7: Match the option.
For insulators the band gap is very high and the conduction band is empty, which is option (1).
\[ \boxed{\text{very high, empty}} \]