During photosynthesis, the process involves the conversion of light energy into chemical energy, primarily resulting in the formation of glucose from carbon dioxide and water. In this process, water is split, and hydrogen is used to help form glucose.
Given the options, the most accurate response to what happened to the radioactive hydrogen during photosynthesis is:
It was recycled when glucose was formed.
This is because the hydrogen atoms from the radioactive water contribute to the formation of glucose, ultimately linking them to the products of photosynthesis.