Which of the following reaction is associated with decarboxylation reactions during the citric acid cycle?
(a) Isocitrate $\to$ $\mathrm{\alpha }$-Ketoglutarate
(b)  $\mathrm{\alpha }$-Ketoglutarate $\to$Succinyl CoA
(c) Succinate $\to$Fumarate
(d) Pyruvate $\to$Acetyl CoA

In Krebs' cycle or citric acid cycle when isocitrate is converted to $\mathrm{\alpha }$-Ketoglutarate and $\mathrm{\alpha }$-Ketoglutarate is converted to succinyl CoA CO₂ is released. When pyruvate is converted to acetyl CoA, then also CO₂ is released but it is a part of link reaction and not Krebs' cycle.