The preparation of 2,4-dinitrophenylhydrazine from hydrazine and 2,4-dinitrochlorobenzene involves a nucleophilic aromatic substitution reaction. Here is the step-by-step reaction mechanism:1. Nucleophilic attack: The nitrogen atom of the hydrazine N2H4 molecule acts as a nucleophile and attacks the electrophilic carbon atom of the 2,4-dinitrochlorobenzene that is bonded to the chlorine atom. This step forms a new carbon-nitrogen bond.2. Formation of a resonance-stabilized intermediate: The electrons from the carbon-chlorine bond move to the chlorine atom, which then forms a negatively charged intermediate. This intermediate is resonance-stabilized due to the delocalization of the negative charge on the chlorine atom and the aromatic ring.3. Proton transfer: A proton from the hydrazine molecule is transferred to the negatively charged chlorine atom, forming a hydrochloric acid HCl molecule as a byproduct.4. Rearomatization: The negatively charged intermediate regains its aromaticity by transferring the negative charge back to the carbon atom, breaking the carbon-chlorine bond, and releasing the chloride ion.5. Protonation of the nitrogen atom: The nitrogen atom in the newly formed 2,4-dinitrophenylhydrazine molecule is protonated by another hydrazine molecule or a solvent molecule, completing the formation of 2,4-dinitrophenylhydrazine.Overall, the reaction can be represented as:N2H4 + C6H3Cl NO2 2 C6H3N2H NO2 2 + HCl