In the above experiment, the alkyl halide acts as a substrate and HO- from KOH as a nucleophile hence this is a nucleophilic substitution reaction.
As the reaction proceeds we get the same amount of product which suggests that the rate of reaction does not depend on the amount of nucleophile.
From this information, we can conclude that this is a unimolecular nucleophilic substitution reaction. Hence the substrate will be a compound from option 2 which can form a stable tertiary carbocation.
Hence option 2 is the correct answer.