Is it possible to draw a reflex angle so the other angle formed by the arm is straight?
Oh, dude, a reflex angle is greater than 180 degrees, so if you draw one arm of the angle straight, the other arm would have to be pointing backwards, which is like, not really a thing in normal geometry. So, technically, no, you can't have a straight angle and a reflex angle sharing an arm. But hey, if you're feeling creative, go for it, who am I to stop you?