Which of the following contains the smallest amount of matter?

A. 250 g

B. 0.25 hg

C. 2500 dg

D. 2.5 kg

A. 250 g contains the smallest amount of matter.

To determine the answer, we write the measurements to its base unit which would be grams. It is written as follows:

A. 250 g

B. 0.25 hg = 25 g

C. 2500 dg = 250 g

D. 2.5 kg = 2500 g

Therefore, the correct answer is option B, 0.25 hg contains the smallest amount of matter.