Question

name the source from which plants obtain hydrogen

Answer 1

Hydrogen in plants is obtained from water absorbed through the plant's roots. The water undergoes photolysis during photosynthesis to produce oxygen and water. Photolysis of water refers to the splitting of water to hydrogen and oxygen with the help of light energy. This process takes place in the first stage of photosynthesis where light energy  is then used in the process of splitting water by use of photons. 

Answer 2

Hydrogen comes from splitting water (H2O) into hydrogen gas and oxygen. Hydrogen is used by plants which combine it with carbon during the photosynthesis process and release oxygen into the atmosphere which is used by all living beings