In a sm viewport, a div defined as <div class="col-md-3 col-lg-7"> will be how many columns wide?

In a standard grid system, such as the one provided by Bootstrap, the total number of columns available is typically 12. The classes assigned to the div, like "col-md-3" and "col-lg-7," define how many of these 12 columns the div will occupy at different viewport sizes.

For the "col-md-3" class, this means that in medium-sized viewports and above, the div will occupy 3 columns of the total 12. The "col-lg-7" class indicates that in large viewports, the div will take up 7 columns. However, when it comes to smaller viewports, if no specific class for small size is provided, the div will default to the standard behavior of occupying the full width, which is all 12 columns.

Therefore, in a small viewport where neither of the specified column sizes applies directly, the div will span all 12 columns by default. This is why the correct answer is that the div is 12 columns wide in a small viewport.