Answer
$n-1$
Work Step by Step
$Insertion$ $sort$ compare first the second element with the first and correctly sorts these two numbers. Then it takes the next element and correctly inserts it in the part of the string that we already know is correctly sorted, and so on.
$First$ $pass$: we compare the first two elements and thus we make 1 comparison.
$Second$ $pass$: We compare the third element with the first element (no other comparisons are needed as the element to insert at the beginning of the already sorted list), thus make 1 comparison.
$Third$ $pass$: We compare the fourth element with the first element, thus we made 1 comparison.
$kth$ $pass$: On the kth pass, we compare the $k+1th$ element with the first terms and thus we make 1 comparison.
Insertion algorithm will step if only 1 element is remaining. If the original list contains n elements, the insertion algorithm will then stop when the $n -1th$ pass (when the nth element is compared with the last n-1 terms).
comparisons $=1+1+1+\ldots+1=\sum_{i=1}^{n-1} 1=n-1$
