Question

why are naphthalene balls stored in air tight packing

Answer 1

naphthalene balls are sublime in nature i.e.when they come in contact with air,they evaporate,directly from solid to gaseous state,without changing into liquid.Therefore they are stored in airtight containers.

Answer 2

when naphthalene balls come in contact with air, they evaporate due to sublimation in which the solid state directly changes into gaseous state,without coming into liquid form. hence..to prevent them from sublimation, they are stored in airtight containers.