Question

Which of these are unit rates
A square yard for every 100 grass seeds
4 acres for 800 plants
2 plants in a square foot
6 plants in 1 square yard
8 seeds per square foot
25 trees per 25 square yards

Answer 1

8 Seeds per Square foot is the answer

Answer 2

a unit rate is any # over 1.

so, 
2 plants in a square foot
6 plants in 1 square yard
8 seeds per square foot
are all unit rates.