Vertical angles are formed when two lines intersect, and they are the angles opposite each other. If ∠1 is one of the angles, the vertical angle to ∠1 would be the angle that is opposite to it.
Without a specific diagram, I can't definitively identify which angle (4, 5, 6, or 7) is the vertical angle to ∠1. However, you would need to look for the angle that is directly across from ∠1 where the two lines intersect to identify the correct vertical angle.
If you can provide more context or a visual reference, I can help further!