NCERT Solutions Curiosity Chapter 10 .2.1 Leaves: the 'food factories' of plants — In-text Question

Sunlight supplies the energy for making food. Chlorophyll in the leaf captures this light energy and uses it to combine carbon dioxide and water into glucose, which is then converted into starch for storage.

Bhaskar's question is answered by Activity 10.3: a leaf from a plant kept in sunlight gives a blue-black colour on its green patches, while a leaf from an identical plant kept in the dark for 36 hours gives no blue-black colour at all. No sunlight means no starch.