Out of the given options, which is not needed in the process of photosynthesis? 1. Chlorophyll 2. Water 3. Sunlight 4. Oxygen

Of the given options, oxygen is not needed for the process of photosynthesis. The chemical reaction for photosynthesis can be written as:

`6 CO_2 + 6 H_2O + sunlight -> C_6H_12O_6 + 6O_2`

In this process, plants (containing chlorophyll pigment) use carbon dioxide and water, in the presence of sunlight, and produce glucose and oxygen. Thus, oxygen is a product of the process and is not required for the process.  

Photosynthesis is the primary production process and is responsible for providing food and oxygen for survival of life on Earth. Organisms use these glucose molecule and break them down into carbon dioxide and water, and generate energy molecules (ATP or adenosine triphosphate), in the process of cellular respiration. 

It is to be noted that plants carry out both photosynthesis and cellular respiration.

Hope this helps.