Compare two neighbours
Goal: Explain what one comparison can fix.
Start with [5,2,4,6,1]. We want the same five values in ascending order. Compare the first neighbours, 5 and 2. Since 5 is larger, swap them: [2,5,4,6,1].
Compare the next neighbours, 5 and 4. Swap again: [2,4,5,6,1]. Comparing 5 and 6 needs no swap. Comparing 6 and 1 does need a swap, giving [2,4,5,1,6].
One pass means a complete scan of the current unsorted part. This left-to-right pass moved its largest value, 6, to the end. The entire array is not sorted yet: 1 is still after 5.
After one left-to-right pass
Which value is guaranteed to be in its final position?
Remember: An ascending pair is in order when the left value is no larger.