Final answer:
RuBisCO attaches O₂ (Oxygen) to RuBP to make phosphoglycolate in a process known as photorespiration, making option (2) the correct answer.
Step-by-step explanation:
The enzyme Ribulose bisphosphate carboxylase-oxygenase (RuBisCO) is crucial in the process of carbon fixation during the Calvin cycle of photosynthesis. RuBisCO typically catalyzes the reaction between CO₂ and Ribulose bisphosphate (RuBP) to form 3-phosphoglycerate (3-PGA), a process which is essential for the production of glucose in plants. However, in conditions of high oxygen concentration or low carbon dioxide concentration, RuBisCO can catalyze the addition of O₂ to RuBP instead, resulting in the formation of phosphoglycolate and 3-PGA in a process known as photorespiration.
Therefore, the correct substance attached to RuBP by RuBisCO to make phosphoglycolate is option (2) O₂ (Oxygen).