Compound 'A' forms phenyl hydrazone, so it must be a carbonyl compound. Since it also gives a negative iodoform test, so it can't be an aldehyde.
'A' on reduction gives propane. So, it must be butanone. Ketone reacts with phenyl hydrazine to form phenyl hydrazone but gives a negative iodoform test.
She will most likely observe that the temperature
does not change during melting because the heat absorbed is used to overcome
intermolecular forces rather than to increase the kinetic energy of the
particles if she measures the temperature of the water in the beaker.