The line AB passes through Quadrant I and Quadrant IV.
When reflected in the x-axis, the y-coordinate of every point is negated. Therefore, the image of the line AB will be in the opposite quadrant with respect to the x-axis.
Point A (3, 5) is in Quadrant I, and its image after reflection in the x-axis will be (3, -5), which lies in Quadrant IV.
Point B (6, 3) is in Quadrant I, and its image after reflection in the x-axis will be (6, -3), which also lies in Quadrant IV.
Therefore, the image of line AB after reflection in the x-axis will lie in Quadrant IV.
Hence, the answer is option D.