Question

1. which pair of angles are vertical angles?

Explanation:

Step1: Recall vertical - angle definition

Vertical angles are formed when two lines intersect. They are non - adjacent angles opposite each other.

Step2: Identify vertical - angle pairs

In the given figure where lines $m$ and $n$ intersect, $\angle1$ and $\angle3$ are non - adjacent and opposite each other, and $\angle2$ and $\angle4$ are non - adjacent and opposite each other.

Answer:

The pairs of vertical angles are $\angle1$ and $\angle3$, $\angle2$ and $\angle4$.