The number of decarboxylations that occur in one turn of citric acid cycle is:

In Krebs cycle there is two successive steps of decarboxylation, leading to the formation of α-ketoglutaric acid and then succinyl-CoA. The conversions are as followsIsocitrate (6C) →α-ketoglutarate (5C) + CO2α-ketoglutarate (5C) → Succinyl CoA(4C) + CO2