Which type of motherboard expansion slot sends data one bit at a time over a serial bus?

The type of motherboard expansion slot that sends data one bit at a time over a serial bus is the PCI Express (PCIe) slot.

Here are the steps to understand why:

1. First, it's important to understand what a motherboard expansion slot is. It's a slot on a motherboard where an expansion card can be inserted. Expansion cards are used to provide or expand on features not offered by the motherboard.

2. Next, we need to understand the difference between serial and parallel data transmission. In serial transmission, data is sent one bit at a time, while in parallel transmission, multiple bits are sent at once.

3. Now, let's look at the different types of motherboard expansion slots. There are several types, including PCI (Peripheral Component Interconnect), AGP (Accelerated Graphics Port), and PCIe (PCI Express).

4. PCI and AGP slots use parallel transmission, meaning they send multiple bits of data at once. On the other hand, PCIe slots use serial transmission, meaning they send one bit of data at a time.

5. Therefore, the type of motherboard expansion slot that sends data one bit at a time over a serial bus is the PCIe slot.