PS is metric or continental horsepower.
It stands for PferdeStarke, which is German for HorsePower
100 horsepower (U.S.) is equal to 101.39 PS
They are close enough to the same that you can more or less use them interchangeably. In Europe, engine power is usually listed as PS or Kw, which is KiloWatts.
PS is the German unit of power, 85 PS means that this car generates 85 PS of power and RXE is the name of the variant. It has got a 110 PS variant also which means that the engine is tuned to generate 110 PS of power.
The petrol variants of Duster and Terrano return a low mileage of around 12-13 kmpl, therefore it is advisable to go with diesel variants. Also, the K9K diesel engine performs better than the 1.6-litre petrol engine.
The procedure of procuring the keys for Renault Duster is a lengthy one. You would have to place a request with Renault service center. A technician would come to your place and unlock the steering and tow it to the service center. Your old lock would be replaced with a new one and new keys would come in 15 days. The cost of the keys would be Rs 4,500 per key. You would also have to take your RC booklet and Insurance papers to your service center.