Question

Is 25 mg lighter or heavier than 25 cg

Answer 1

Well 

1 cg (centigram) is the same as 10 mg (milligrams) 

so

25 milligrams are lighter

Answer 2

1 centigram= 10 milligram 

if you convert 25cg to mg, you'll get 250mg (25×10)
so 25 mg is lighter than 25cg(250mg)

so your answer is 25mg is lighter than 25cg.