Answer-
1 and 2 are congruent because they are a pair of corresponding angles
Solution-
When two lines are crossed by another line (called the transversal), the angles in matching corners are called Corresponding Angles.
The parallel case -
If the transversal cuts across parallel lines, then corresponding angles have the same measure.
The non-parallel case -
If the transversal cuts across lines that are not parallel, the corresponding angles have no particular relationship to each other.
In the given diagram, 1 and 2 are a pair of corresponding angles. And as the two lines are parallel, so 1 and 2 are congruent.