if 3 chemical compounds have the same melting point how can you tell the difference?

Answer 1

check the physical changes like color or check to see if the have diffrent temperatures after the melt or cool

Answer 2

I suppose you mean that two or three of the compounds could be identical, and one or none different. For the sake of the argument, let the compounds be called A, B, and C. Take a bit of A, and mix it with a bit each of B and C. Take the melting points of the mixtures A-B and A-C. If the melting point of A-B is the same as A, then they are identical. If it is lower, they are different. Similarly for A-C. Also, take a bit of B and mix it with bits of A and C. Repeat the process. You should be able to reason out which are identical (same melting point in a mixture of the two) and which different (lower melting point).

Answer 3

Check solubility and density.