Final answer:
HCN is the acid among the given options that will have the strongest conjugate base, because HCN is a weaker acid compared to H2SO4, HNO3, and HBr, which are strong acids.
Step-by-step explanation:
The question poses which of the following acids will have the strongest conjugate base: HCN, H2SO4, KCl, HNO3, and HBr. To determine this, we consider the principle that the weaker the acid, the stronger its conjugate base. H2SO4, HNO3, and HBr are all classified as strong acids, meaning their conjugate bases are very weak. However, HCN (hydrocyanic acid) is known to be a weaker acid than the former ones, thus its conjugate base, the cyanide ion (CN-), is stronger in comparison. Therefore, HCN will have the strongest conjugate base among the given options.