The diagram where angles 1 and 2 form a linear pair is the 2nd diagram.
It should be noted that a linear pair simply means a pair of adjacent angles that is formed when there are two lines which intersect each other.
It should also be noted that in a linear pair, the adjacent angles create a line and the total angle is equal to 180°.
Based on the description given, we can see that the second diagram fits the scenario and the sum of its angles equal to 180° since there are 2 right angles.
