The question asks to identify the type of code counter that prevents ambiguity during state transitions.

Understanding State Transition Ambiguity

In sequential logic circuits like counters, ambiguity arises when multiple bits change their state simultaneously during a transition from one value to the next. This can lead to temporary, incorrect intermediate states, causing errors.

Gray Code Counter Solution

The Gray code counter is specifically designed to overcome this challenge.

• Key Property: In Gray code, only one bit changes between any two adjacent code words. For example, transitioning from 00 to 01 changes only the last bit; transitioning from 01 to 11 changes only the second bit.
• Ambiguity Prevention: Because only a single bit changes at a time, there are no invalid intermediate states during a transition. This ensures smooth and unambiguous state changes.

Why Other Codes Cause Ambiguity

• Binary Code Counter: Standard binary codes often change multiple bits simultaneously. For instance, going from 011 (3) to 100 (4) requires all three bits to change.
• BCD (Binary Coded Decimal) and Excess-3 Code Counters: While used for specific encoding, these also exhibit multi-bit changes between consecutive numbers (e.g., 0111 to 1000 in BCD), potentially causing ambiguity similar to standard binary.

Therefore, the Gray code counter is the suitable choice for removing ambiguity during state transitions.