Q.Photosynthesis is described as a means of "autotrophic nutrition" because a photosynthetic organism:

[!TLDR]

Autotrophic nutrition means an organism synthesises its own organic food from inorganic raw materials (CO2 + water) using light energy, rather than consuming ready-made organic food.

[!ANSWER]

(b) synthesises its own organic food from simple inorganic raw materials using light energy

Autotrophs ("self-nourishing") are distinguished from heterotrophs precisely by not needing to consume other organisms for organic food. A photosynthesising plant takes in only inorganic raw materials -- CO2 from the air and water from the soil -- and, using the light energy trapped by chlorophyll, builds these into energy-rich organic carbohydrate. This self-sufficiency in manufacturing food is exactly what the term "autotrophic nutrition" describes, and it is why photosynthesis is the defining biochemical process of plant nutrition.

[!ANSWER]

(b) synthesises its own organic food from simple inorganic raw materials using light energy

Recall the literal meaning of "autotroph" -- self + nourishing -- and match it to the option describing self-manufactured food from inorganic starting materials.

Confusing autotrophic nutrition with saprotrophic nutrition (absorbing already-digested organic matter) -- the defining feature of autotrophy is starting from purely inorganic raw materials.