Understanding the Question: We need to identify which counter uses 5 flip-flops to count up to 31 (a MOD-31 counter).
Key Formulas and approach: Different counters have different capacities per flip-flop ($n$):
Binary/Ripple: States $= 2^n$
Ring Counter: States $= n$
Johnson Counter: States $= 2n$
Detailed Solution:
Step 1: Calculating for Binary. For a counter to reach 31, it must have at least 31 states. $2^5 = 32$. This matches the 5 flip-flop requirement.
Step 2: Checking other types. A Ring counter would need 31 flip-flops. A Johnson counter would need 16 flip-flops ($2 \times 16 = 32$).
Step 3: Identifying the correct type. The binary logic (where $n$ flip-flops give $2^n$ states) is used by Asynchronous (Ripple) and Synchronous counters. Given the options, the Asynchronous counter is the standard answer.
Conclusion: The Asynchronous (Ripple) counter is correct.