Which by-product would be obtained in high yield if
thediazotization of p-toluidine were carried out at 30 c instead
of0-5 c?

The byproduct is mostly p-cresol, which is p-methylphenol.

Explanation:

Because of the many hydrolysis of the diazonium salts that would occur since the temperature of the reaction is greater than 0-5°C, there would be the formation of p-cresol as one of the byproducts, and it is of the highest yield among the three byproducts formed.

Simple Explanation of the Reaction Process:

The process starts from the diazotization of p-toluidine to form diazonium salt as an intermediate.

The reaction would then be quenched by urea and what follows subsequently is the hydrolysis of the diazonium salts to give p-cresol in high yield.