Is it permissible to sell a share of an inheritance in an apartment, provided that it is vacated after the mother's death, and is Zakat on the money due on the apartment's price before it is received?

There is no objection to selling your share in the apartment for the agreed-upon price. However, the exclusion of the usufruct of the sold property for the duration of the mother's life renders the condition void, because the duration is unknown. If the contract is ruled valid and the condition void, and the seller insists on it, the buyer has the right to annul the sale. As for zakat (definition), if you leave the price with the buyer and he is willing to pay it, then zakat is due on it if it reaches the nisab (definition) and a full year has passed. However, if the debt is owed by a defaulter or an insolvent person, zakat is only due upon its receipt for one year.