Q.What is Pseudo first order reaction? Derive integrated rate law equation for zero order reaction.

A pseudo first order reaction's true molecularity is masked by one reactant being present in vast excess; the zero-order rate law integrates to a simple linear expression.

Pseudo first order reaction: a reaction that is intrinsically of a higher order (commonly second order, involving two reactants) but experimentally behaves as first order because one of the reactants is present in such large excess (or acts as the solvent) that its concentration remains effectively constant throughout the reaction; only the other reactant's concentration change is kinetically significant. Example: acid-catalysed hydrolysis of ethyl acetate in the presence of a large excess of water, rate $= k'[CH_3COOC_2H_5]$ (with $[H_2O]$ absorbed into the constant $k'$).

Derivation of the zero-order integrated rate law: for a zero-order reaction, rate is independent of concentration:

…