We can start by plotting the points on a coordinate plane and then drawing the trapezoid:
```
G (2,1) F (6,1)
+--------------+
| |
| |
| |
D (2,3) E (4,3)
```
We can see that the trapezoid has a base of length 4 (the distance between points D and E), and a height of 2 (the distance between points E and F, or D and G).
Therefore, the area of the trapezoid is:
```
(1/2) * (base1 + base2) * height
= (1/2) * (4 + 4) * 2
= 8
```
So the area of trapezoid DEFG is 8 square units. Therefore, the answer is (B) 8 square units.