During photosynthesis the oxygen in glucose is from

Explanation-

In (1985), Cornelius Van Neil experimented to report that oxygen released during photosynthesis is formed from the photolysis of water. While he worked on the purple and green bacteria, he found photosynthesis is essentially a light-dependent reaction, that includes hydrogen from certain oxidizable compounds reduces carbon dioxide to carbohydrates-

2H2A + CO2 →2A + CH2O + H2O
                    Light


Later, in the year 1941, Ruben and Kamen confirmed that the source of oxygen in the photosynthetic reaction is Hydrogen and not carbon dioxide. They used isotopic oxygen 18O for this purpose.
The equation includes-

6CO2 + 12H2O18 →→C6H12O6 + 6H2O +6O218


Final Answer-

So, The correct option is A.