How is zakat paid on two plots of land that were purchased in installments for the purpose of real estate investment, knowing that 100,000 has been paid and the intention has changed to selling them as land with a profit, and they have not yet been sold?

If you purchased land with the intention of selling it after building on it, then it is a trade asset subject to zakat. It should be valued at the completion of a Hijri year from the original capital, and one-quarter of one-tenth (2.5%) of its value should be paid. Zakat is due on it every year as long as it has not been sold, and the obligation of zakat does not lapse with the passing of years.

As for the outstanding installments, they are deducted from the value of the land when it is appraised for the year, unless you have other funds sufficient to cover them. This is because debt, according to the majority of scholars, reduces zakat on hidden assets. However, some jurists hold that it does not reduce it, and this is more cautious and more absolving of responsibility.