The melting point of the product was found to be 94 C. This is very close to 95 C, the melting point of 1,2-dimethoxy-4-nitrobenzene, so this is very likely to be the product. Also, according to melting point the product is quite pure.
The filtrate mother liquor has not been run on TLC, so no semi-quantitative data on the relative purities of the crude product and the recrystallised product have been obtained.
So the product is 1,2-dimethoxy-4-nitrobenzene, consistent with the melting point.
The melting point of the semicarbazide derivative of compound A was found to be 224-225 C, which means that compound A is likely to be o-chloro-benzaldehyde or p-hydroxy-benzaldehyde. According to the 1HNMR spectrum, with benzene proton peaks around 7 ppm and aldehyde proton singlet, the second functional group should also contain one proton, showing up as a singlet. Therefore, the second functional group is a hydroxy-group, so compound A is p-hydroxy-benzaldehyde. This hydroxyl-group also gives the possibility to from the bicyclic structure of compound B.
The H atom of NH will exchange with solvent, so if D2O is added it may be replaced with D. This only influences the peak of the H of NH, which will become a doublet with the second peak (of D) at lower intensity and at higher field (lower ).