In short, what you want is 5 */\ i.10
5 */\ i.10
0 120 720 2520 6720 15120
However, if you ever run across this issue in another context, and you really want to address the rows, you could say:
]M=:5>\i. 10
0 1 2 3 4
1 2 3 4 5
2 3 4 5 6
3 4 5 6 7
4 5 6 7 8
5 6 7 8 9
*/ rows M
0 120 720 2520 6720 15120
Rows is defined by the standard library as "1
. That is, it applies the verb at "rank 1". Rank is a fundamental concept in J, and you'll need to understand it to progress with the language.