31. Catalysis in Organic Reactions

Name the carbonyl containing product formed when propyl-3-methylpentanoate reacts with Mg²⁺ in an aqueous solution. 

Given below are the pK_a values of metal ions after binding to water. If the greater the acidity of a metal cation then the more easily the complex forms, which of the following ions would facilitate the fastest basic hydrolysis of ethyl propanoate?