I have a row of elements, and have a second row of elements below it. I am trying to keep both the tables in view of the user. At what row count should I ideally introduce a scroll?
It does not have a straightforward answer. The criteria for showing scroll depending on the number of rows is not a good idea. How will you handle this in different devices with different screen resolutions, size, orientation? In these cases, your basic requirement to keep both the tables in the view of the user will not be fulfilled.
I would suggest you don't show the scroll at all. Rather, keep a definite number of rows and a pagination/more button. On click of the button, you can show the next set of rows in the same view by appending them or by replacing them with new data ( Just like the Google Search results)