An unknown compound X is one of the four compounds listed in the table below. A mixture of X with o-toluic acid melts at 100 degrees Celsius, a mixture of X with benzoic acid melts at 112 degrees Celsius, a mixture of X with phenyl succinate melts at 110 degrees Celsius, and a mixture of X with m-aminophenol melts at 115 degrees Celsius. Give the identity of X and explain your reasoning.

Compound, melting point:
o-toluic acid, 102 degrees Celsius
benzoic acid, 121 degrees Celsius
phenyl succinate, 121 degrees Celsius
m-aminophenol, 122 degrees Celsius

To find the identity of compound X, we need to compare the melting points of X mixed with different compounds to the melting points of those individual compounds.

Let's analyze the given information:

1. A mixture of X with o-toluic acid melts at 100 degrees Celsius.
- The melting point of o-toluic acid alone is 102 degrees Celsius. The observed melting point of the mixture is lower than that of o-toluic acid, indicating that X reduces the overall melting point of the mixture.

2. A mixture of X with benzoic acid melts at 112 degrees Celsius.
- The melting point of benzoic acid alone is 121 degrees Celsius. The observed melting point of the mixture is lower than that of benzoic acid, suggesting that X reduces the overall melting point of the mixture.

3. A mixture of X with phenyl succinate melts at 110 degrees Celsius.
- The melting point of phenyl succinate alone is 121 degrees Celsius. Again, the observed melting point of the mixture is lower than that of phenyl succinate, indicating that X decreases the overall melting point.

4. A mixture of X with m-aminophenol melts at 115 degrees Celsius.
- The melting point of m-aminophenol alone is 122 degrees Celsius. The observed melting point of the mixture is lower than that of m-aminophenol, indicating that X reduces the overall melting point of the mixture.

From the information above, we can conclude that compound X reduces the melting point of all the mixtures it forms. This suggests that compound X is likely an impurity, or a substance with a lower melting point than the other compounds.

Given that all the individual compounds have higher melting points than X mixed with any of them, we can infer that the lowest melting point among these mixtures will correspond to the melting point of compound X.

Comparing the given melting points of the mixtures:
- Mixture of X with o-toluic acid melts at 100 degrees Celsius.
- Mixture of X with benzoic acid melts at 112 degrees Celsius.
- Mixture of X with phenyl succinate melts at 110 degrees Celsius.
- Mixture of X with m-aminophenol melts at 115 degrees Celsius.

We can see that the lowest melting point observed is 100 degrees Celsius, which corresponds to the mixture of X with o-toluic acid.

Therefore, compound X is most likely o-toluic acid.