(d) 3 units
Since the y-coordinates are equal, $PQ = \left|\dfrac{11}{3} - \dfrac{2}{3}\right| = \dfrac{9}{3} = 3$ units.
Source: Chapter 7, Section 7.2 (Distance Formula)
When two points have the same y-coordinate, the distance is simply the absolute difference of the x-coordinates. No need for the full distance formula. Watch for fractions — subtract carefully: $\frac{11}{3} - \frac{2}{3} = \frac{9}{3} = 3$.