Answer: The correct option is triangle GDC
Step-by-step explanation: Please refer to the picture attached for further details.
The dimensions give for the cube are such that the top surface has vertices GBCF while the bottom surface has vertices HADE.
A right angle can be formed in quite a number of ways since the cube has right angles on all six surfaces. However the question states that the diagonal that forms the right angle runs "through the interior."
Therefore option 1 is not correct since the diagonal formed in triangle BDH passes through two surfaces. Triangle DCB is also formed with its diagonal passing only along one of the surfaces. Triangle GHE is also formed with its diagonal running through one of the surfaces.
However, triangle GDC is formed with its diagonal passing through the interior as shown by the "zigzag" line from point G to point D. And then you have another line running from vertex D to vertex C.
