To solve this problem, we need to determine the number of substrate level phosphorylations that occur in one turn of the citric acid cycle.$\newline$Let's analyze the citric acid cycle:$\newline \bullet$The citric acid cycle, also known as the Krebs cycle, is a series of chemical reactions used by all aerobic organisms to generate energy.$\newline \bullet$During one turn of the citric acid cycle, several reactions occur, but only one involves substrate level phosphorylation.$\newline \bullet$This specific reaction is the conversion of succinyl-CoA to succinate.$\newline \bullet$In this step, succinyl-CoA is converted to succinate by the enzyme succinyl-CoA synthetase.$\newline \bullet$This reaction results in the formation of GTP (or ATP, depending on the organism) from GDP and inorganic phosphate (Pi).$\newline$Therefore, there is one substrate level phosphorylation in one turn of the citric acid cycle.$\newline$Thus, the correct answer is Option 1: One.