Final answer:
The correct sequence for the Calvin cycle is carbon fixation, followed by reduction, and then the regeneration of RuBP, as illustrated in the stages of the Calvin cycle.
Step-by-step explanation:
The correct order of molecular conversions in the Calvin cycle is carbon fixation, reduction, and regeneration of RuBP. During the first stage, carbon fixation, the enzyme RuBisCO incorporates CO₂ into an organic molecule by attaching it to RuBP to form 3-PGA. Next, in the reduction phase, the 3-PGA molecules are reduced using ATP and NADPH to produce G3P, which is a three-carbon sugar. Finally, in the regeneration phase, the molecule RuBP, which starts the cycle, is regenerated from G3P so that the cycle can continue. Therefore, the correct answer is option (a) Carbon fixation, reduction, regeneration of RuBP, consistent with the stages outlined in the provided reference information.