Bootstrap 4 correct way to use row and col classes [duplicate]

Answer 1

For the second row instead of that should I have to wrap that button inside a column. Like this

Yes, only a Bootstrap column is allowed to be a direct child of a Bootstrap row.

So, in every Bootstrap row, you must have at least one Bootstrap column and all of your content must go into Bootstrap columns and never into Bootstrap rows directly.

This is because Bootstrap rows and columns are designed to work in pairs i.e. no content may ever be placed directly into a Bootstrap row. Only Bootstrap columns may be direct children of Bootstrap rows.

Reference:

https://getbootstrap.com/docs/4.0/layout/grid/