Imine formation is an acid-catalyzed process, however the procedure performed in this does not require the addition of an external acid. Suggest a viable source of acid in the reaction depicted.

See explaination

Explanation:

Reaction between p- toluidine and o- vaniline to form imine.This reaction does occur in the presence of a acidic source.

Here the -OH group in the o- vaniline is quite acidic so it acts a internal acidic catalyst. Hence the reaction occurred in the absence of any external acidic source.The reaction mechanism is given at the attached file.

please kindly see attachment.

is there any options? maybe im just not seeing them but i need the options to

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catya your not at all which answer i've seen you do this on another question!