Which class is used for the last column of multiple columns in a Bootstrap grid?

The correct choice reflects the convention established in Bootstrap for managing grid column configurations. In Bootstrap, the "portlet-column-last" class is specifically designed to denote the last column in a series of columns within a layout. This is significant for achieving the desired styling and spacing, ensuring that elements align properly according to Bootstrap's responsive grid system.

Using the "portlet-column-last" class informs the CSS framework that this column is the final one in its respective row. As a result, it can apply any necessary margin adjustments or styling specific to the last column, which enhances the overall structure and presentation of the grid.

The other options are not utilized in Bootstrap for this specific purpose. "Portlet-column-first" would correlate with the first column, while "portlet-column-only" suggests exclusivity without addressing any last or other positional significance. "Portlet-column-middle" implies a central position but does not concern itself with markings for the end of a column set. Thus, the choice of "portlet-column-last" is aligned with Bootstrap’s grid management conventions and supports the intended layout benefits.