In terms of band theory, what is the difference between
a. a condcutor and an insulator
b. a conductor and a semiconductor

Explanation

To answer the question regarding the differences between a conductor and an insulator, as well as between a conductor and a semiconductor in terms of band theory, we can break it down step by step.

### Step-by-Step Solution

**Step 1: Understanding Energy Bands**
- In solids, electrons occupy energy levels that are grouped into bands. The two most important bands are the **valence band** (where electrons are normally present) and the **conduction band** (where electrons can move freely and conduct electricity).
- The **energy band gap** is the energy difference between the valence band and the conduction band.

...