Question

why photosynthesis is called as carbon assimilation process​

Answer 1

Answer:

Carbon fixation or сarbon assimilation is the conversion process of inorganic carbon (carbon dioxide) to organic compounds by living organisms. The most prominent example is photosynthesis, although chemosynthesis is another form of carbon fixation that can take place in the absence of sunlight.

Answer 2

Photosynthesis is the process by which plants prepare their food in the presence of sunlight using water and carbon dioxide as the raw materials.

The products formed are Glucose , oxygen and energy.
So you see how a simple CO2 molecule is yielding a complex compound which is glucose.
Thus we say it is a carbon assimilation or carbon collection process.