Final answer:
The missing justification in the table is that corresponding angles formed by a transversal on parallel lines are supplementary.
Step-by-step explanation:
The missing justification is d. Corresponding angles formed by a transversal on parallel lines are supplementary.
In the given table, angle 2 and angle 6 are alternate interior angles, which are equal because the vertical angles formed by angle 2 are congruent. Similarly, angle 4 and angle 6 are equal because they are vertical angles. Therefore, angle 4 is equal to angle 6. This justifies the statement that angle 2 is equal to angle 6.