Question

explain why naphthalene balls kept in store cloth in our home disppear over a period of time

Answer 1

You know that when a drop of water falls on hot object it undergoes evaporation and turns into water vapour. This phase transition is from liquid state to gaseous/vapour state. You know water is solid below 0 degree centigrade and if you keep it(ICE) at room temperature it eventually melts. This process is called melting and if water is made to reach 100 degrees it will boil. LIKE WISE NAPHTHALENE BALL UNDERGOES SUBLIMATION(PROCESS IN WHICH SOLID SUBSTANCE CHANGES ITS PHASE TO GAS WITHOUT PASSING THROUGH LIQUID PHASE). Unlike ice(water) where it first gets converted to liquid ,later to gas/vapour. 
Since naphthalene balls(solid) slowly undergo sublimation at room temperature, it is directly converted to gaseous state,leaving behind neither liquid nor solid trace.

Answer 2

because they directly convert their state from solid to gas and when they convert into gas they mix with air and disappear