Given below are two statements.
Statement I: Photosynthesis is essentially a light-dependent reaction in which hydrogen from a suitable oxidizable compound reduces carbon dioxide to carbohydrates. 
Statement II: In green plants, H₂O is the hydrogen donor and is oxidized to O₂.
In light of the above statements, choose the correct answer from the options given below.

Cornelius van Niel (1897-1985),  demonstrated that photosynthesis is essentially a light-dependent reaction in which hydrogen from a suitable oxidizable compound reduces carbon dioxide to carbohydrates. 

In green plants, H₂O is the hydrogen donor and is oxidised to O₂.

 Some organisms do not release O2 during photosynthesis. When H₂S, instead is the hydrogen donor for purple and green sulphur bacteria, the ‘oxidation’ product is sulphur or sulphate depending on the organism, and not O₂. 

Hence, he inferred that the O₂ evolved by the green plant comes from H₂O, not carbon dioxide. This was later proved by using radioisotopic techniques.