An udentified substance, y, was thought to be one of the following three compounds.

compound: a
melting point: 132 °c

compound: b
melting point: 133 °c

compound: c
melting point: 134 °c

y was mixed with each of the above compounds and the melting point of each mixture was determined. the following results were obtained.

mixture: y + a
melting point: 114 – 129 °c

mixture: y + b
melting point: 132 – 133 °c

mixture: y + c
melting point: 86 – 99 °c

deduce the identity of y. briefly explain your answer.