Who discovered that light is essential for releasing oxygen in plants?

The hypothesis that all photosynthetic organisms require a source of hydrogen was first proposed by

Moll's half leaf experiment was done to show ...................... was required for photosynthesis.

Name the scientist who demonstrated the effect of different wavelengths of light on photosynthesis using green algae and aerobic bacteria.

Who demonstrated that photosynthesis is essentially a light dependent reaction in which hydrogen from a suitable oxidisable compound reduces $CO_2$ to carbohydrates?

Which isotope is used to study photosynthesis?