Answer : The correct option is, (A) the copper must have combined with another substance.
Explanation :
According to the question, when a sample of copper powder is heated in an evaporating dish by using Bunsen burner then the mass of the powder in the evaporating dish increases after heating that means the copper powder will be combined with the another substance.
If the mass of powder in the evaporating dish is decreases after the heating then the copper powder must have lost some matter.
The given option C and D are wrong statements because the hot copper is less dense than the cold copper and as we know that the density is directly proportional to the mass of a substance that means the hot copper weighs less than cold copper.
Hence, the correct option is, (A) the copper must have combined with another substance.