Right angle has a 45 degree angle which is perpendicular.
Number 2 would be the correct answer
Let's see what the answer choices mean with respect to the requirement to prove a triangle is a right triangle.
a) two sides are congruent: the triangle is isosceles, but not necessarily a right triangle.
b) two sides are perpendicular: the triangle must be a right triangle.
c) three sides are congruent: the triangle is equilateral so is definitely not a right triangle.
d) sides are parallel: the figure cannot be a triangle.
The appropriate choice is the second one ...
... Use the slope formula to see if any sides are perpendicular.
B. Use the slope formula to see if any sides are perpendicular