Keep in mind that the tangent function is negative in Quadrants II and IV.
Of the three possible answers, the 2nd is invalid because the tangent is positive in Q III.
If the reference angle were in Quadrant II and had the value 30° (second possible answer), then the opposite side would be +1, the adjacent side -√3 and the hypotenuse 2. Based on this, the tangent of theta would be opp / adj, or +1 / (-√3) or -√3/3. This is correct.
