Answer :
To solve this questions we need to know the heterocyclic compounds and little bit about resonance. Therefore the nitrogen which is labelled 2 will react first with acid.
What is heterocyclic compound?
Heterocyclic compounds are those cyclic organic compounds that contains hetero atoms in place of carbon like N,S and O.
Pyrazole contains has structure just like pyrrole the Nitrogen which is labelled 1 that is NH act like nitrogen of pyrrole and the nitrogen that is labelled as 2 act like nitrogen of pyridine.
The electron of NH is involved in resonance, it is not free to give its electron to hydrogen ion from acid. So the nitrogen which is like nitrogen of pyridine will take hydrogen ion from acid first.
Therefore the nitrogen which is labelled 2 will react first with acid.
To know more about heterocyclic compounds, here:
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