Answer:
The answer to your question is sample A and sample C.
Explanation:
Melting point is a physical property of substances, physical properties do not depend on the amount of matter, so it doesn't matter that in one sample we have 5 kg and in the other we have 2 kg.
Besides in samples B and C we have the same amount of matter, they are different substances(copper and iron) so, their melting points are different.
Also, in samples A and D, we have the same amount of matter, but they are different substances so their melting points are different.
