For any counter:-
- There are a certain number of Flip Flops from which it is built.
- There are a certain number of states that the counter can be in. Each state represents a unique value.
Synchronous Counters:
$n$ Flip Flops count $2^n$ different values.
Or you can say that $n$ Flip Flops result in $2^n$ states, and each state represents a distinguishable value.
Asynchronous Counters (aka Ripple Counters):
$n$ Flip Flops count $2^n$ different values.
Or you can say that $n$ Flip Flops result in $2^n$ states, and each state represents a distinguishable value.
Johnson Counter: (aka Twisted Ring Counter, Switch-Tail Ring Counter)
$n$ Flip Flops count $2n$ different values.
Or you can say that $n$ Flip Flops result in $2n$ states, and each state represents a distinguishable value.
Ring Counters:
$n$ Flip Flops count $n$ different values.
Or you can say that $n$ Flip Flops result in $n$ states, and each state represents a distinguishable value.
Now unless explicitly mentioned otherwise, a ring counter should be assumed as a straight ring counter, which leads us to Option B