The correct option is C Stroma
The non pigmented part of the chloroplast is the stroma. Lamellae of chloroplasts are known as thylakoids. A thylakoid is a membrane-bound compartment inside chloroplasts and cyanobacteria. They are the site of the light-dependent reactions of photosynthesis. Thylakoids consist of a thylakoid membrane surrounding a thylakoid lumen. Chloroplast thylakoids frequently form stacks of disks referred to as grana. Grana are connected by intergranal or stroma thylakoids, which join granum stacks together as a single functional compartment. These stroma do not possess any pigment.