Let's consider a full circular$-$indexing array $($aka circular buffer$)$ queue as illustrated in the fgure below. The illustrated queue is FULL and we have omitted drawing the index, meaning its size equals the length of the array.

Remember that there are multiple ways to implement a circular array queue. In this implementation, is the index of the element at the front of the queue, and is the index of the element at the end of the queue $($not the next empty location$).$

Given the current value of back index $(0),$ and the status of the queue $($it is full$),$ which element will be returned by the next call of the dequeue operation on the illustrated queue?

$50$

$60$

We don't have enough information to decide.

$70$