The first unstable compound formed during C3 cycle is: (a) 3-carboxy,2-keto, 1,6 bi phosphorobitol
(c) 2-carboxy,3-keto,1,5 biphosphorobitol
(b) 2-carboxy,3-keto,1,5-biphosphorobit ol
(d) 3-carboxy,3-keto, 1,6-biphosphorobitol​

(b) 2-carboxy,3-keto,1,5-biphosphorobitol

Explanation:

2-carboxy, 3-keto, 1,5-biphosphorobitol is the first unstable molecule formed during the C3 cycle. Due to its instability, this molecule is quickly broken down into two molecules each containing 3 carbon atoms, called 3-phosphoglyceric acid, this breakdown is done through water in a process known as hydrolysis.