In $\mathrm{C}_3$ plants, the first stable product of photosynthesis during the dark reaction is:

The first stable product of $\mathrm{CO}_2$ fixation in $\mathrm{C}_3$ plants is a three-carbon organic acid. The enzyme ribulose-1,5-bisphosphate carboxylase-oxygenase (RuBisCO) combines $\mathrm{CO}_2$ with the ribulose 1,5-bisphosphate to form two molecules of 3-phosphoglyceric acid. Related Theory $A D P, N A D P$, and glucose are the end products of the $C_3$ cycle. ADP and NADP are produced in the first stage of $\mathrm{C}_3$ cycle. In the second stage, glucose is produced.