The 5-C compound formed during TCA cycle is 

During the tricarboxylic acid (TCA) cycle, also known as the citric acid cycle or Krebs cycle, the 5-carbon compound formed is alpha-ketoglutaric acid. It is formed when the 6-carbon isocitric acid undergoes oxidative decarboxylation, releasing carbon dioxide (CO₂) and forming alpha-ketoglutaric acid.

(2) Oxalo-succinic acid is a six-carbon compound.

(3) Succinic acid, also known as succinate, is a 4-carbon compound and an intermediate in the TCA cycle. It is not
         the 5-C compound formed during the cycle.

(4) Fumaric acid is a 4-carbon compound and also an intermediate in the TCA cycle. It is not the 5-C compound
         formed during the cycle.