Does zakat become obligatory on a debtor's possessions, which include a portion of a house, a share in a debt-ridden factory, and a sum of money in the bank, taking into consideration the Murabaha loan he took to purchase a dwelling, and the fact that he does not own a dwelling and lives in rented accommodation while helping his parents?

The fundamental principle is that Zakat is obligatory on money if it reaches the نصاب (minimum threshold) and a Ḥawl (lunar year) passes over it. The intention to buy a house does not negate the obligation of Zakat. Regarding debts to the bank, if the debtor does not possess anything beyond his needs that corresponds to the debt, then he is permitted to deduct the value of the debt from the money on which Zakat became obligatory, and he should pay Zakat on the remainder if it does not fall below the نصاب.