Explanation:
Naphthalene is actually a solid substance which tends to undergo sublimation due to its high vapor pressure. But when it is kept under vaccum of under an oven then actually we can store naphthalene for a long time.
This is because air present in vacum or under the oven does not contain any vapors. Hence, napthalene does not get consumed.
Thus, we can conclude that if you place naphthalene under vacuum or in an oven for several hours to dry it then we can store it for longer period of time.