Since the slope of a vertical line is undefined, is it possible for vertical lines to be parallel. (Explain)

Yes the slope of a vertical line is parallel.

Parallel lines never intersect each other.

Y-axis is a vertical axis cartesian coordinate plane.

All vertical lines would be parallel to y-axis.

Because all vertical lines would have same slope, that is undefined slope.

Therefore, all vertical lines would be parallel lines.

So, we can finally say that it is possible for vertical lines to be parallel.