Final answer:
Glycogen is stored in the cytosol of a cell, which is the fluid component of the cytoplasm where various metabolites and enzymes are present.
Step-by-step explanation:
Glycogen, a form of stored glucose, is primarily found within cytosol of a cell. Cytosol is the fluid part of the cytoplasm and contains an aqueous solution of electrolytes and enzymes, vital for various cellular processes. Unlike organelles such as mitochondria, which produce energy, or the smooth endoplasmic reticulum, which synthesizes lipids and carbohydrates, the cytosol serves as a storage and metabolic compartment for compounds like glycogen. Therefore, the correct answer to where inside a cell glycogen is stored is C) cytosol.