*Question E7A03:
Which of the following can divide the frequency of a pulse train by 2?*  

*Correct Answer is  B: A flip-flop*  

### AI Response: (may contain errors)  

A flip-flop is the correct answer for dividing the frequency of a pulse train by 2. Here's why:

1. **Why the correct answer is correct:**
   - A flip-flop is a digital circuit that can store a single bit of data. When configured as a "toggle flip-flop," it changes state (from 0 to 1 or from 1 to 0) on each incoming pulse. This means that for every two input pulses, the output changes once, effectively dividing the frequency of the input pulse train by 2.

2. **Why the other choices are incorrect:**
   - **An XOR gate (Choice A):** An XOR gate outputs true only when the inputs are different. It does not inherently divide frequency; it performs logical operations based on input states.
   - **An OR gate (Choice C):** An OR gate outputs true if at least one input is true. Like the XOR gate, it does not divide frequency but performs logical operations.
   - **A multiplexer (Choice D):** A multiplexer selects one of several input signals and forwards the selected input to a single output line. It does not divide frequency; it is used for routing signals.

3. **Useful concept:**
   - **Toggle Flip-Flop Operation:** If you have a pulse train with a frequency $f_{\text{in}}$, a toggle flip-flop will produce an output frequency $f_{\text{out}} = \frac{f_{\text{in}}}{2}$.

Understanding how a flip-flop works is crucial for digital circuit design and frequency division applications.