Question

Merits And demerits Of Permanent land Revenue

Answer 1

If you are talking about British law
then
Merits to Britishers was -           The system would ensure regular flow of revenue  and zamindars would invest in improving land quality
Demerit were     -  1) zamindars were not interested in improving land
                                2)when the prices rose and cultivation expanded ,the zamindars benefited                                             whereas  no profit to Britishers.
                                3)revenues were too high for peasants to pay to the zamindars and if failed 
                                    they were evicted from land

 hope it was what you wanted and helped you