What is the zakat due on a property purchased with the intention of renting it out, and which was rented for 40,000 dirhams, paid in installments (10,000 dirhams every 3 months)?

Zakat is not obligatory on the rented property itself. Rather, it is obligatory on the rent (revenue) if it reaches the nisab (threshold) and a full year has passed over it, either individually or by adding it to other funds.