Identify two conjugate base for each compound HCN and HBr

Which statement is usually true about the relationship between activation energy and reaction rates? low activation energy barriers result in low rates. high activation energy barriers result in low rates. low activation energy barriers result in no reaction. high activation energy barriers result in no reaction.

An experimental procedure requires a 10 ml of acid to be dissolved

In the diagram here that represents the reaction, which reactant, a or b, is the limiting reagent?