Small delay occurs between the clock edge and the flip flop output, Q becoming valid

The delay you're referring to is known as propagation delay. Here's a step-by-step explanation:

1. When a flip-flop receives a signal from the clock edge, it doesn't instantly process this signal. There's a small delay before the flip-flop responds.

2. This delay is known as the propagation delay. It's the time taken for the input change to propagate through the flip-flop and cause a change at the output.

3. The propagation delay is a crucial factor in synchronous systems like flip-flops. It determines the maximum speed at which the flip-flop can operate.

4. If the next clock edge arrives before the propagation delay is over, the flip-flop may not respond correctly to the input signal. This can lead to issues like race conditions.

5. Therefore, the clock frequency should be low enough to allow the flip-flop to process each signal before the next one arrives. This ensures that the output, Q, is valid and reliable.