As westerly winds blow over a north-south oriented mountain range, the airflow is deflected in such a way that a trough forms on the side of the mountain

The correct answer is - east.
When the westerly winds flow into a north-south mountain range they will hit the west side of the mountain range, since they are a wind that comes from the west and moves to the east, while the east side of the mountain will get a downward wind on it's slops, that'll be dry and also much weaker and less intense.

1.0 larger it be exact

I'm pretty sure it's c. extremely gradual but not 100% sure though.