Answer :

We know that miligram is lighter than a centigram ⇒ 25 mg < 25 cg
Well,

The prefix "milli" means thousandth and the prefix "centi" means hundredth.  So a milligram will be one-tenth of a centigram.

10 mg. = 1 cg.
25 mg. = 2.5 cg.

2.5 cg. < 25 cg.

25 mg. is lighter than 25 cg.